diff --git a/crates/icrate/src/fixes/Foundation/copying.rs b/crates/icrate/src/fixes/Foundation/copying.rs
index b0d7c8ef4..4f8f4183a 100644
--- a/crates/icrate/src/fixes/Foundation/copying.rs
+++ b/crates/icrate/src/fixes/Foundation/copying.rs
@@ -22,7 +22,6 @@ extern_protocol!(
         #[optional]
         fn copy(&self) -> Id<Self::Immutable>
         where
-            Self: Sized,
             Self: CounterpartOrSelf;
 
         /// Returns a new instance that's a copy of the receiver.
@@ -37,7 +36,6 @@ extern_protocol!(
         #[method_id(copyWithZone:)]
         unsafe fn copyWithZone(&self, zone: *mut NSZone) -> Id<Self::Immutable>
         where
-            Self: Sized,
             Self: CounterpartOrSelf;
     }
 
@@ -65,7 +63,6 @@ extern_protocol!(
         #[optional]
         fn mutableCopy(&self) -> Id<Self::Mutable>
         where
-            Self: Sized,
             Self: CounterpartOrSelf;
 
         /// Returns a new instance that's a mutable copy of the receiver.
@@ -80,7 +77,6 @@ extern_protocol!(
         #[method_id(mutableCopyWithZone:)]
         unsafe fn mutableCopyWithZone(&self, zone: *mut NSZone) -> Id<Self::Mutable>
         where
-            Self: Sized,
             Self: CounterpartOrSelf;
     }
 
diff --git a/crates/objc2/CHANGELOG.md b/crates/objc2/CHANGELOG.md
index e604ad0f5..931643621 100644
--- a/crates/objc2/CHANGELOG.md
+++ b/crates/objc2/CHANGELOG.md
@@ -22,6 +22,10 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 * Added `Allocated::set_ivars`, which sets the instance variables of an
   object, and returns the new `rc::PartialInit`.
 * Added the ability for `msg_send_id!` to call `super` methods.
+* Implement `Send` and `Sync` for `ProtocolObject` if the underlying protocol
+  implements it.
+* Added ability to create `Send` and `Sync` versions of
+  `ProtocolObject<dyn NSObjectProtocol>`.
 
 ### Changed
 * **BREAKING**: Changed how instance variables work in `declare_class!`.
@@ -149,6 +153,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 * **BREAKING**: Make `rc::Allocated` allowed to be `NULL` internally, such
   that uses of `Option<Allocated<T>>` is now simply `Allocated<T>`.
 * `AnyObject::class` now returns a `'static` reference to the class.
+* Relaxed `ProtocolType` requirement on `ProtocolObject`.
 
 ### Deprecated
 * Soft deprecated using `msg_send!` without a comma between arguments (i.e.
diff --git a/crates/objc2/src/macros/extern_protocol.rs b/crates/objc2/src/macros/extern_protocol.rs
index 5418fb52a..1a99770a0 100644
--- a/crates/objc2/src/macros/extern_protocol.rs
+++ b/crates/objc2/src/macros/extern_protocol.rs
@@ -184,7 +184,7 @@ macro_rules! __inner_extern_protocol {
         $(#[$impl_m])*
         unsafe impl<T> $name for $crate::runtime::ProtocolObject<T>
         where
-            T: ?$crate::__macro_helpers::Sized + $crate::ProtocolType + $name
+            T: ?$crate::__macro_helpers::Sized + $name
         {}
 
         // SAFETY: The specified name is ensured by caller to be a protocol,
@@ -204,6 +204,9 @@ macro_rules! __inner_extern_protocol {
         {
             const __INNER: () = ();
         }
+
+        // TODO: Should we also implement `ImplementedBy` for `Send + Sync`
+        // types, as is done for `NSObjectProtocol`?
     };
 }
 
diff --git a/crates/objc2/src/mutability.rs b/crates/objc2/src/mutability.rs
index f2d707ecb..0bc764084 100644
--- a/crates/objc2/src/mutability.rs
+++ b/crates/objc2/src/mutability.rs
@@ -33,7 +33,7 @@
 use core::marker::PhantomData;
 
 use crate::runtime::{AnyObject, ProtocolObject};
-use crate::{ClassType, Message, ProtocolType};
+use crate::{ClassType, Message};
 
 mod private_mutability {
     pub trait Sealed {}
@@ -269,7 +269,7 @@ mod private_traits {
 }
 
 impl<T: ?Sized + ClassType> private_traits::Sealed for T {}
-impl<P: ?Sized + ProtocolType> private_traits::Sealed for ProtocolObject<P> {}
+impl<P: ?Sized> private_traits::Sealed for ProtocolObject<P> {}
 impl private_traits::Sealed for AnyObject {}
 
 /// Marker trait for classes where [`Id::clone`] is safe.
@@ -303,7 +303,7 @@ impl MutabilityIsIdCloneable for InteriorMutable {}
 impl MutabilityIsIdCloneable for MainThreadOnly {}
 
 unsafe impl<T: ?Sized + ClassType> IsIdCloneable for T where T::Mutability: MutabilityIsIdCloneable {}
-unsafe impl<P: ?Sized + ProtocolType + IsIdCloneable> IsIdCloneable for ProtocolObject<P> {}
+unsafe impl<P: ?Sized + IsIdCloneable> IsIdCloneable for ProtocolObject<P> {}
 // SAFETY: Same as for root classes.
 unsafe impl IsIdCloneable for AnyObject {}
 
@@ -336,7 +336,7 @@ impl MutabilityIsRetainable for InteriorMutable {}
 impl MutabilityIsRetainable for MainThreadOnly {}
 
 unsafe impl<T: ?Sized + ClassType> IsRetainable for T where T::Mutability: MutabilityIsRetainable {}
-unsafe impl<P: ?Sized + ProtocolType + IsRetainable> IsRetainable for ProtocolObject<P> {}
+unsafe impl<P: ?Sized + IsRetainable> IsRetainable for ProtocolObject<P> {}
 
 /// Marker trait for classes that can be allocated from any thread.
 ///
@@ -367,10 +367,7 @@ unsafe impl<T: ?Sized + ClassType> IsAllocableAnyThread for T where
     T::Mutability: MutabilityIsAllocableAnyThread
 {
 }
-unsafe impl<P: ?Sized + ProtocolType + IsAllocableAnyThread> IsAllocableAnyThread
-    for ProtocolObject<P>
-{
-}
+unsafe impl<P: ?Sized + IsAllocableAnyThread> IsAllocableAnyThread for ProtocolObject<P> {}
 
 /// Marker trait for classes that may feasibly be used behind a mutable
 /// reference.
@@ -401,7 +398,7 @@ unsafe impl<T: ?Sized + ClassType> IsAllowedMutable for T where
     T::Mutability: MutabilityIsAllowedMutable
 {
 }
-unsafe impl<P: ?Sized + ProtocolType + IsAllowedMutable> IsAllowedMutable for ProtocolObject<P> {}
+unsafe impl<P: ?Sized + IsAllowedMutable> IsAllowedMutable for ProtocolObject<P> {}
 // SAFETY: Same as for root classes.
 unsafe impl IsAllowedMutable for AnyObject {}
 
@@ -430,7 +427,7 @@ impl MutabilityIsMutable for Mutable {}
 impl<IS: ?Sized> MutabilityIsMutable for MutableWithImmutableSuperclass<IS> {}
 
 unsafe impl<T: ?Sized + ClassType> IsMutable for T where T::Mutability: MutabilityIsMutable {}
-unsafe impl<P: ?Sized + ProtocolType + IsMutable> IsMutable for ProtocolObject<P> {}
+unsafe impl<P: ?Sized + IsMutable> IsMutable for ProtocolObject<P> {}
 
 /// Marker trait for classes that are only available on the main thread.
 ///
@@ -455,7 +452,7 @@ unsafe impl<T: ?Sized + ClassType> IsMainThreadOnly for T where
     T::Mutability: MutabilityIsMainThreadOnly
 {
 }
-unsafe impl<P: ?Sized + ProtocolType + IsMainThreadOnly> IsMainThreadOnly for ProtocolObject<P> {}
+unsafe impl<P: ?Sized + IsMainThreadOnly> IsMainThreadOnly for ProtocolObject<P> {}
 
 /// Marker trait for classes whose `hash` and `isEqual:` methods are stable.
 ///
@@ -489,7 +486,7 @@ impl<MS: ?Sized> MutabilityHashIsStable for ImmutableWithMutableSubclass<MS> {}
 impl<IS: ?Sized> MutabilityHashIsStable for MutableWithImmutableSuperclass<IS> {}
 
 unsafe impl<T: ?Sized + ClassType> HasStableHash for T where T::Mutability: MutabilityHashIsStable {}
-unsafe impl<P: ?Sized + ProtocolType + HasStableHash> HasStableHash for ProtocolObject<P> {}
+unsafe impl<P: ?Sized + HasStableHash> HasStableHash for ProtocolObject<P> {}
 
 /// Retrieve the immutable/mutable counterpart class, and fall back to `Self`
 /// if not applicable.
@@ -589,7 +586,7 @@ where
     type Mutable = <T::Mutability as private_counterpart::MutabilityCounterpartOrSelf<T>>::Mutable;
 }
 
-unsafe impl<P: ?Sized + ProtocolType> CounterpartOrSelf for ProtocolObject<P> {
+unsafe impl<P: ?Sized> CounterpartOrSelf for ProtocolObject<P> {
     // SAFETY: The only place where this would differ from `Self` is for
     // classes with `MutableWithImmutableSuperclass<IS>`.
     //
diff --git a/crates/objc2/src/runtime/nsobject.rs b/crates/objc2/src/runtime/nsobject.rs
index 3672a5c85..deb48c856 100644
--- a/crates/objc2/src/runtime/nsobject.rs
+++ b/crates/objc2/src/runtime/nsobject.rs
@@ -7,6 +7,8 @@ use crate::runtime::{AnyClass, AnyObject, ProtocolObject};
 use crate::{extern_methods, msg_send, msg_send_id, Message};
 use crate::{ClassType, ProtocolType};
 
+use super::ImplementedBy;
+
 /// The root class of most Objective-C class hierarchies.
 ///
 /// This represents the [`NSObject` class][cls]. The name "NSObject" also
@@ -163,6 +165,33 @@ crate::__inner_extern_protocol!(
     ("NSObject")
 );
 
+// SAFETY: Anything that implements `NSObjectProtocol` and is `Send` is valid
+// to convert to `ProtocolObject<dyn NSObjectProtocol + Send>`.
+unsafe impl<T> ImplementedBy<T> for dyn NSObjectProtocol + Send
+where
+    T: ?Sized + Message + NSObjectProtocol + Send,
+{
+    const __INNER: () = ();
+}
+
+// SAFETY: Anything that implements `NSObjectProtocol` and is `Sync` is valid
+// to convert to `ProtocolObject<dyn NSObjectProtocol + Sync>`.
+unsafe impl<T> ImplementedBy<T> for dyn NSObjectProtocol + Sync
+where
+    T: ?Sized + Message + NSObjectProtocol + Sync,
+{
+    const __INNER: () = ();
+}
+
+// SAFETY: Anything that implements `NSObjectProtocol` and is `Send + Sync` is
+// valid to convert to `ProtocolObject<dyn NSObjectProtocol + Send + Sync>`.
+unsafe impl<T> ImplementedBy<T> for dyn NSObjectProtocol + Send + Sync
+where
+    T: ?Sized + Message + NSObjectProtocol + Send + Sync,
+{
+    const __INNER: () = ();
+}
+
 unsafe impl NSObjectProtocol for NSObject {}
 
 extern_methods!(
diff --git a/crates/objc2/src/runtime/protocol_object.rs b/crates/objc2/src/runtime/protocol_object.rs
index 46ff46c29..384ebf99c 100644
--- a/crates/objc2/src/runtime/protocol_object.rs
+++ b/crates/objc2/src/runtime/protocol_object.rs
@@ -7,7 +7,7 @@ use crate::encode::{Encoding, RefEncode};
 use crate::rc::{autoreleasepool_leaking, Id};
 use crate::runtime::__nsstring::nsstring_to_str;
 use crate::runtime::{AnyObject, NSObjectProtocol};
-use crate::{Message, ProtocolType};
+use crate::Message;
 
 /// An internal helper trait for [`ProtocolObject`].
 ///
@@ -57,25 +57,35 @@ pub unsafe trait ImplementedBy<T: ?Sized + Message> {
 /// ```
 #[doc(alias = "id")]
 #[repr(C)]
-pub struct ProtocolObject<P: ?Sized + ProtocolType> {
+pub struct ProtocolObject<P: ?Sized> {
     inner: AnyObject,
     p: PhantomData<P>,
 }
 
+// SAFETY: `Send` if the underlying trait promises `Send`.
+//
+// E.g. `ProtocolObject<dyn NSObjectProtocol + Send>` is naturally `Send`.
+unsafe impl<P: ?Sized + Send> Send for ProtocolObject<P> {}
+
+// SAFETY: `Sync` if the underlying trait promises `Sync`.
+//
+// E.g. `ProtocolObject<dyn NSObjectProtocol + Sync>` is naturally `Sync`.
+unsafe impl<P: ?Sized + Sync> Sync for ProtocolObject<P> {}
+
 // SAFETY: The type is `#[repr(C)]` and `AnyObject` internally
-unsafe impl<P: ?Sized + ProtocolType> RefEncode for ProtocolObject<P> {
+unsafe impl<P: ?Sized> RefEncode for ProtocolObject<P> {
     const ENCODING_REF: Encoding = Encoding::Object;
 }
 
 // SAFETY: The type is `AnyObject` internally, and is mean to be messaged
 // as-if it's an object.
-unsafe impl<P: ?Sized + ProtocolType> Message for ProtocolObject<P> {}
+unsafe impl<P: ?Sized> Message for ProtocolObject<P> {}
 
-impl<P: ?Sized + ProtocolType> ProtocolObject<P> {
+impl<P: ?Sized> ProtocolObject<P> {
     /// Get an immutable type-erased reference from a type implementing a
     /// protocol.
     #[inline]
-    pub fn from_ref<T: Message>(obj: &T) -> &Self
+    pub fn from_ref<T: ?Sized + Message>(obj: &T) -> &Self
     where
         P: ImplementedBy<T>,
     {
@@ -89,7 +99,7 @@ impl<P: ?Sized + ProtocolType> ProtocolObject<P> {
     /// Get a mutable type-erased reference from a type implementing a
     /// protocol.
     #[inline]
-    pub fn from_mut<T: Message>(obj: &mut T) -> &mut Self
+    pub fn from_mut<T: ?Sized + Message>(obj: &mut T) -> &mut Self
     where
         P: ImplementedBy<T>,
     {
@@ -118,7 +128,7 @@ impl<P: ?Sized + ProtocolType> ProtocolObject<P> {
     }
 }
 
-impl<P: ?Sized + ProtocolType + NSObjectProtocol> PartialEq for ProtocolObject<P> {
+impl<P: ?Sized + NSObjectProtocol> PartialEq for ProtocolObject<P> {
     #[inline]
     #[doc(alias = "isEqual:")]
     fn eq(&self, other: &Self) -> bool {
@@ -126,16 +136,16 @@ impl<P: ?Sized + ProtocolType + NSObjectProtocol> PartialEq for ProtocolObject<P
     }
 }
 
-impl<P: ?Sized + ProtocolType + NSObjectProtocol> Eq for ProtocolObject<P> {}
+impl<P: ?Sized + NSObjectProtocol> Eq for ProtocolObject<P> {}
 
-impl<P: ?Sized + ProtocolType + NSObjectProtocol> hash::Hash for ProtocolObject<P> {
+impl<P: ?Sized + NSObjectProtocol> hash::Hash for ProtocolObject<P> {
     #[inline]
     fn hash<H: hash::Hasher>(&self, state: &mut H) {
         self.__hash().hash(state);
     }
 }
 
-impl<P: ?Sized + ProtocolType + NSObjectProtocol> fmt::Debug for ProtocolObject<P> {
+impl<P: ?Sized + NSObjectProtocol> fmt::Debug for ProtocolObject<P> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         // Attempt to format description string
         if let Some(description) = self.__description() {
@@ -159,10 +169,9 @@ impl<P: ?Sized + ProtocolType + NSObjectProtocol> fmt::Debug for ProtocolObject<
     }
 }
 
-impl<P, T> AsRef<ProtocolObject<T>> for ProtocolObject<P>
+impl<P: ?Sized, T> AsRef<ProtocolObject<T>> for ProtocolObject<P>
 where
-    P: ?Sized + ProtocolType,
-    T: ?Sized + ProtocolType + ImplementedBy<ProtocolObject<P>>,
+    T: ?Sized + ImplementedBy<ProtocolObject<P>>,
 {
     #[inline]
     fn as_ref(&self) -> &ProtocolObject<T> {
@@ -170,10 +179,9 @@ where
     }
 }
 
-impl<P, T> AsMut<ProtocolObject<T>> for ProtocolObject<P>
+impl<P: ?Sized, T> AsMut<ProtocolObject<T>> for ProtocolObject<P>
 where
-    P: ?Sized + ProtocolType,
-    T: ?Sized + ProtocolType + ImplementedBy<ProtocolObject<P>>,
+    T: ?Sized + ImplementedBy<ProtocolObject<P>>,
 {
     #[inline]
     fn as_mut(&mut self) -> &mut ProtocolObject<T> {
@@ -181,7 +189,7 @@ where
     }
 }
 
-// TODO: Maybe iplement Borrow + BorrowMut?
+// TODO: Maybe implement Borrow + BorrowMut?
 
 #[cfg(test)]
 #[allow(clippy::missing_safety_doc)]
@@ -194,7 +202,9 @@ mod tests {
     use super::*;
     use crate::mutability::Mutable;
     use crate::runtime::{NSObject, NSObjectProtocol};
-    use crate::{declare_class, extern_methods, extern_protocol, ClassType, DeclaredClass};
+    use crate::{
+        declare_class, extern_methods, extern_protocol, ClassType, DeclaredClass, ProtocolType,
+    };
 
     extern_protocol!(
         unsafe trait Foo {
@@ -264,6 +274,9 @@ mod tests {
     unsafe impl FooBar for DummyClass {}
     // unsafe impl FooFooBar for DummyClass {}
 
+    unsafe impl Send for DummyClass {}
+    unsafe impl Sync for DummyClass {}
+
     extern_methods!(
         unsafe impl DummyClass {
             #[method_id(new)]
@@ -275,6 +288,12 @@ mod tests {
     fn impl_traits() {
         assert_impl_all!(NSObject: NSObjectProtocol);
         assert_impl_all!(ProtocolObject<dyn NSObjectProtocol>: NSObjectProtocol);
+        assert_not_impl_any!(ProtocolObject<dyn NSObjectProtocol>: Send, Sync);
+        assert_impl_all!(ProtocolObject<dyn NSObjectProtocol + Send>: NSObjectProtocol, Send);
+        assert_not_impl_any!(ProtocolObject<dyn NSObjectProtocol + Send>: Sync);
+        assert_impl_all!(ProtocolObject<dyn NSObjectProtocol + Sync>: NSObjectProtocol, Sync);
+        assert_not_impl_any!(ProtocolObject<dyn NSObjectProtocol + Sync>: Send);
+        assert_impl_all!(ProtocolObject<dyn NSObjectProtocol + Send + Sync>: NSObjectProtocol, Send, Sync);
         assert_not_impl_any!(ProtocolObject<dyn Foo>: NSObjectProtocol);
         assert_impl_all!(ProtocolObject<dyn Bar>: NSObjectProtocol);
         assert_impl_all!(ProtocolObject<dyn FooBar>: NSObjectProtocol);
@@ -332,6 +351,10 @@ mod tests {
         let _nsobject: &ProtocolObject<dyn NSObjectProtocol> = ProtocolObject::from_ref(bar);
         let nsobject: &ProtocolObject<dyn NSObjectProtocol> = ProtocolObject::from_ref(&*obj);
         let _nsobject: &ProtocolObject<dyn NSObjectProtocol> = ProtocolObject::from_ref(nsobject);
+        let _: &ProtocolObject<dyn NSObjectProtocol + Send> = ProtocolObject::from_ref(&*obj);
+        let _: &ProtocolObject<dyn NSObjectProtocol + Sync> = ProtocolObject::from_ref(&*obj);
+        let _: &ProtocolObject<dyn NSObjectProtocol + Send + Sync> =
+            ProtocolObject::from_ref(&*obj);
 
         let _foobar: &mut ProtocolObject<dyn FooBar> = ProtocolObject::from_mut(&mut *obj);
         let _foobar: Id<ProtocolObject<dyn FooBar>> = ProtocolObject::from_id(obj);
diff --git a/crates/test-ui/ui/protocol_object_only_protocols.rs b/crates/test-ui/ui/protocol_object_only_protocols.rs
new file mode 100644
index 000000000..03980b90d
--- /dev/null
+++ b/crates/test-ui/ui/protocol_object_only_protocols.rs
@@ -0,0 +1,27 @@
+//! Ensure that `ProtocolObject` cannot be incorrectly constructed.
+use icrate::Foundation::NSCopying;
+use objc2::runtime::{NSObject, NSObjectProtocol, ProtocolObject};
+
+trait Foo {
+    fn foo(&self) {}
+}
+
+impl<T: ?Sized> Foo for T {}
+
+fn main() {
+    let obj = NSObject::new();
+    let _: &ProtocolObject<NSObject> = ProtocolObject::from_ref(&*obj);
+    let _: &ProtocolObject<dyn Send> = ProtocolObject::from_ref(&*obj);
+    let _: &ProtocolObject<dyn Foo> = ProtocolObject::from_ref(&*obj);
+
+    // `NSObject` is neither `Send` nor `Sync`.
+    let _: &ProtocolObject<dyn NSObjectProtocol + Send> = ProtocolObject::from_ref(&*obj);
+    let _: &ProtocolObject<dyn NSObjectProtocol + Sync> = ProtocolObject::from_ref(&*obj);
+    let _: &ProtocolObject<dyn NSObjectProtocol + Send + Sync> = ProtocolObject::from_ref(&*obj);
+
+    // `NSObject` is not `NSCopying`.
+    let _: &ProtocolObject<dyn NSCopying> = ProtocolObject::from_ref(&*obj);
+
+    // `dyn NSCopying + Send` does not implement `ImplementedBy` (yet).
+    let _: &ProtocolObject<dyn NSCopying + Send> = ProtocolObject::from_ref(&*obj);
+}
diff --git a/crates/test-ui/ui/protocol_object_only_protocols.stderr b/crates/test-ui/ui/protocol_object_only_protocols.stderr
new file mode 100644
index 000000000..038ea3af0
--- /dev/null
+++ b/crates/test-ui/ui/protocol_object_only_protocols.stderr
@@ -0,0 +1,333 @@
+error[E0277]: the trait bound `NSObject: ImplementedBy<NSObject>` is not satisfied
+ --> ui/protocol_object_only_protocols.rs
+  |
+  |     let _: &ProtocolObject<NSObject> = ProtocolObject::from_ref(&*obj);
+  |                                        ------------------------ ^^^^^ the trait `ImplementedBy<NSObject>` is not implemented for `NSObject`
+  |                                        |
+  |                                        required by a bound introduced by this call
+  |
+  = help: the following other types implement trait `ImplementedBy<T>`:
+            (dyn NSObjectProtocol + 'static)
+            (dyn NSObjectProtocol + Send + 'static)
+            (dyn NSObjectProtocol + Sync + 'static)
+            (dyn NSObjectProtocol + Send + Sync + 'static)
+            (dyn NSAccessibilityColor + 'static)
+            (dyn NSAccessibilityCustomRotorItemSearchDelegate + 'static)
+            (dyn NSAccessibilityElementProtocol + 'static)
+            (dyn NSAccessibilityGroup + 'static)
+          and $N others
+note: required by a bound in `ProtocolObject::<P>::from_ref`
+ --> $WORKSPACE/crates/objc2/src/runtime/protocol_object.rs
+  |
+  |     pub fn from_ref<T: ?Sized + Message>(obj: &T) -> &Self
+  |            -------- required by a bound in this associated function
+  |     where
+  |         P: ImplementedBy<T>,
+  |            ^^^^^^^^^^^^^^^^ required by this bound in `ProtocolObject::<P>::from_ref`
+
+error[E0277]: the trait bound `dyn Send: ImplementedBy<NSObject>` is not satisfied
+ --> ui/protocol_object_only_protocols.rs
+  |
+  |     let _: &ProtocolObject<dyn Send> = ProtocolObject::from_ref(&*obj);
+  |                                        ------------------------ ^^^^^ the trait `ImplementedBy<NSObject>` is not implemented for `dyn Send`
+  |                                        |
+  |                                        required by a bound introduced by this call
+  |
+  = help: the following other types implement trait `ImplementedBy<T>`:
+            (dyn NSObjectProtocol + 'static)
+            (dyn NSObjectProtocol + Send + 'static)
+            (dyn NSObjectProtocol + Sync + 'static)
+            (dyn NSObjectProtocol + Send + Sync + 'static)
+            (dyn NSAccessibilityColor + 'static)
+            (dyn NSAccessibilityCustomRotorItemSearchDelegate + 'static)
+            (dyn NSAccessibilityElementProtocol + 'static)
+            (dyn NSAccessibilityGroup + 'static)
+          and $N others
+note: required by a bound in `ProtocolObject::<P>::from_ref`
+ --> $WORKSPACE/crates/objc2/src/runtime/protocol_object.rs
+  |
+  |     pub fn from_ref<T: ?Sized + Message>(obj: &T) -> &Self
+  |            -------- required by a bound in this associated function
+  |     where
+  |         P: ImplementedBy<T>,
+  |            ^^^^^^^^^^^^^^^^ required by this bound in `ProtocolObject::<P>::from_ref`
+
+error[E0277]: the trait bound `dyn Foo: ImplementedBy<NSObject>` is not satisfied
+ --> ui/protocol_object_only_protocols.rs
+  |
+  |     let _: &ProtocolObject<dyn Foo> = ProtocolObject::from_ref(&*obj);
+  |                                       ------------------------ ^^^^^ the trait `ImplementedBy<NSObject>` is not implemented for `dyn Foo`
+  |                                       |
+  |                                       required by a bound introduced by this call
+  |
+  = help: the following other types implement trait `ImplementedBy<T>`:
+            (dyn NSObjectProtocol + 'static)
+            (dyn NSObjectProtocol + Send + 'static)
+            (dyn NSObjectProtocol + Sync + 'static)
+            (dyn NSObjectProtocol + Send + Sync + 'static)
+            (dyn NSAccessibilityColor + 'static)
+            (dyn NSAccessibilityCustomRotorItemSearchDelegate + 'static)
+            (dyn NSAccessibilityElementProtocol + 'static)
+            (dyn NSAccessibilityGroup + 'static)
+          and $N others
+note: required by a bound in `ProtocolObject::<P>::from_ref`
+ --> $WORKSPACE/crates/objc2/src/runtime/protocol_object.rs
+  |
+  |     pub fn from_ref<T: ?Sized + Message>(obj: &T) -> &Self
+  |            -------- required by a bound in this associated function
+  |     where
+  |         P: ImplementedBy<T>,
+  |            ^^^^^^^^^^^^^^^^ required by this bound in `ProtocolObject::<P>::from_ref`
+
+error[E0277]: `*const UnsafeCell<()>` cannot be sent between threads safely
+ --> ui/protocol_object_only_protocols.rs
+  |
+  |     let _: &ProtocolObject<dyn NSObjectProtocol + Send> = ProtocolObject::from_ref(&*obj);
+  |                                                           ------------------------ ^^^^^ `*const UnsafeCell<()>` cannot be sent between threads safely
+  |                                                           |
+  |                                                           required by a bound introduced by this call
+  |
+  = help: within `NSObject`, the trait `Send` is not implemented for `*const UnsafeCell<()>`
+  = help: the following other types implement trait `ImplementedBy<T>`:
+            (dyn NSObjectProtocol + 'static)
+            (dyn NSObjectProtocol + Send + 'static)
+            (dyn NSObjectProtocol + Sync + 'static)
+            (dyn NSObjectProtocol + Send + Sync + 'static)
+            (dyn NSAccessibilityColor + 'static)
+            (dyn NSAccessibilityCustomRotorItemSearchDelegate + 'static)
+            (dyn NSAccessibilityElementProtocol + 'static)
+            (dyn NSAccessibilityGroup + 'static)
+          and $N others
+  = note: required because it appears within the type `(*const UnsafeCell<()>, PhantomPinned)`
+note: required because it appears within the type `PhantomData<(*const UnsafeCell<()>, PhantomPinned)>`
+ --> $RUST/core/src/marker.rs
+  |
+  | pub struct PhantomData<T: ?Sized>;
+  |            ^^^^^^^^^^^
+note: required because it appears within the type `UnsafeCell<PhantomData<(*const UnsafeCell<()>, PhantomPinned)>>`
+ --> $RUST/core/src/cell.rs
+  |
+  | pub struct UnsafeCell<T: ?Sized> {
+  |            ^^^^^^^^^^
+note: required because it appears within the type `objc_object`
+ --> $WORKSPACE/crates/objc-sys/src/object.rs
+  |
+  | pub struct objc_object {
+  |            ^^^^^^^^^^^
+note: required because it appears within the type `AnyObject`
+ --> $WORKSPACE/crates/objc2/src/runtime/mod.rs
+  |
+  | pub struct AnyObject(ffi::objc_object);
+  |            ^^^^^^^^^
+note: required because it appears within the type `NSObject`
+ --> $WORKSPACE/crates/objc2/src/runtime/nsobject.rs
+  |
+  | pub struct NSObject {
+  |            ^^^^^^^^
+  = note: required for `dyn NSObjectProtocol + Send` to implement `ImplementedBy<NSObject>`
+note: required by a bound in `ProtocolObject::<P>::from_ref`
+ --> $WORKSPACE/crates/objc2/src/runtime/protocol_object.rs
+  |
+  |     pub fn from_ref<T: ?Sized + Message>(obj: &T) -> &Self
+  |            -------- required by a bound in this associated function
+  |     where
+  |         P: ImplementedBy<T>,
+  |            ^^^^^^^^^^^^^^^^ required by this bound in `ProtocolObject::<P>::from_ref`
+
+error[E0277]: `UnsafeCell<PhantomData<(*const UnsafeCell<()>, PhantomPinned)>>` cannot be shared between threads safely
+ --> ui/protocol_object_only_protocols.rs
+  |
+  |     let _: &ProtocolObject<dyn NSObjectProtocol + Sync> = ProtocolObject::from_ref(&*obj);
+  |                                                           ------------------------ ^^^^^ `UnsafeCell<PhantomData<(*const UnsafeCell<()>, PhantomPinned)>>` cannot be shared between threads safely
+  |                                                           |
+  |                                                           required by a bound introduced by this call
+  |
+  = help: within `NSObject`, the trait `Sync` is not implemented for `UnsafeCell<PhantomData<(*const UnsafeCell<()>, PhantomPinned)>>`
+  = help: the following other types implement trait `ImplementedBy<T>`:
+            (dyn NSObjectProtocol + 'static)
+            (dyn NSObjectProtocol + Send + 'static)
+            (dyn NSObjectProtocol + Sync + 'static)
+            (dyn NSObjectProtocol + Send + Sync + 'static)
+            (dyn NSAccessibilityColor + 'static)
+            (dyn NSAccessibilityCustomRotorItemSearchDelegate + 'static)
+            (dyn NSAccessibilityElementProtocol + 'static)
+            (dyn NSAccessibilityGroup + 'static)
+          and $N others
+note: required because it appears within the type `objc_object`
+ --> $WORKSPACE/crates/objc-sys/src/object.rs
+  |
+  | pub struct objc_object {
+  |            ^^^^^^^^^^^
+note: required because it appears within the type `AnyObject`
+ --> $WORKSPACE/crates/objc2/src/runtime/mod.rs
+  |
+  | pub struct AnyObject(ffi::objc_object);
+  |            ^^^^^^^^^
+note: required because it appears within the type `NSObject`
+ --> $WORKSPACE/crates/objc2/src/runtime/nsobject.rs
+  |
+  | pub struct NSObject {
+  |            ^^^^^^^^
+  = note: required for `dyn NSObjectProtocol + Sync` to implement `ImplementedBy<NSObject>`
+note: required by a bound in `ProtocolObject::<P>::from_ref`
+ --> $WORKSPACE/crates/objc2/src/runtime/protocol_object.rs
+  |
+  |     pub fn from_ref<T: ?Sized + Message>(obj: &T) -> &Self
+  |            -------- required by a bound in this associated function
+  |     where
+  |         P: ImplementedBy<T>,
+  |            ^^^^^^^^^^^^^^^^ required by this bound in `ProtocolObject::<P>::from_ref`
+
+error[E0277]: `UnsafeCell<PhantomData<(*const UnsafeCell<()>, PhantomPinned)>>` cannot be shared between threads safely
+ --> ui/protocol_object_only_protocols.rs
+  |
+  |     let _: &ProtocolObject<dyn NSObjectProtocol + Send + Sync> = ProtocolObject::from_ref(&*obj);
+  |                                                                  ------------------------ ^^^^^ `UnsafeCell<PhantomData<(*const UnsafeCell<()>, PhantomPinned)>>` cannot be shared between threads safely
+  |                                                                  |
+  |                                                                  required by a bound introduced by this call
+  |
+  = help: within `NSObject`, the trait `Sync` is not implemented for `UnsafeCell<PhantomData<(*const UnsafeCell<()>, PhantomPinned)>>`
+  = help: the following other types implement trait `ImplementedBy<T>`:
+            (dyn NSObjectProtocol + 'static)
+            (dyn NSObjectProtocol + Send + 'static)
+            (dyn NSObjectProtocol + Sync + 'static)
+            (dyn NSObjectProtocol + Send + Sync + 'static)
+            (dyn NSAccessibilityColor + 'static)
+            (dyn NSAccessibilityCustomRotorItemSearchDelegate + 'static)
+            (dyn NSAccessibilityElementProtocol + 'static)
+            (dyn NSAccessibilityGroup + 'static)
+          and $N others
+note: required because it appears within the type `objc_object`
+ --> $WORKSPACE/crates/objc-sys/src/object.rs
+  |
+  | pub struct objc_object {
+  |            ^^^^^^^^^^^
+note: required because it appears within the type `AnyObject`
+ --> $WORKSPACE/crates/objc2/src/runtime/mod.rs
+  |
+  | pub struct AnyObject(ffi::objc_object);
+  |            ^^^^^^^^^
+note: required because it appears within the type `NSObject`
+ --> $WORKSPACE/crates/objc2/src/runtime/nsobject.rs
+  |
+  | pub struct NSObject {
+  |            ^^^^^^^^
+  = note: required for `dyn NSObjectProtocol + Send + Sync` to implement `ImplementedBy<NSObject>`
+note: required by a bound in `ProtocolObject::<P>::from_ref`
+ --> $WORKSPACE/crates/objc2/src/runtime/protocol_object.rs
+  |
+  |     pub fn from_ref<T: ?Sized + Message>(obj: &T) -> &Self
+  |            -------- required by a bound in this associated function
+  |     where
+  |         P: ImplementedBy<T>,
+  |            ^^^^^^^^^^^^^^^^ required by this bound in `ProtocolObject::<P>::from_ref`
+
+error[E0277]: `*const UnsafeCell<()>` cannot be sent between threads safely
+ --> ui/protocol_object_only_protocols.rs
+  |
+  |     let _: &ProtocolObject<dyn NSObjectProtocol + Send + Sync> = ProtocolObject::from_ref(&*obj);
+  |                                                                  ------------------------ ^^^^^ `*const UnsafeCell<()>` cannot be sent between threads safely
+  |                                                                  |
+  |                                                                  required by a bound introduced by this call
+  |
+  = help: within `NSObject`, the trait `Send` is not implemented for `*const UnsafeCell<()>`
+  = help: the following other types implement trait `ImplementedBy<T>`:
+            (dyn NSObjectProtocol + 'static)
+            (dyn NSObjectProtocol + Send + 'static)
+            (dyn NSObjectProtocol + Sync + 'static)
+            (dyn NSObjectProtocol + Send + Sync + 'static)
+            (dyn NSAccessibilityColor + 'static)
+            (dyn NSAccessibilityCustomRotorItemSearchDelegate + 'static)
+            (dyn NSAccessibilityElementProtocol + 'static)
+            (dyn NSAccessibilityGroup + 'static)
+          and $N others
+  = note: required because it appears within the type `(*const UnsafeCell<()>, PhantomPinned)`
+note: required because it appears within the type `PhantomData<(*const UnsafeCell<()>, PhantomPinned)>`
+ --> $RUST/core/src/marker.rs
+  |
+  | pub struct PhantomData<T: ?Sized>;
+  |            ^^^^^^^^^^^
+note: required because it appears within the type `UnsafeCell<PhantomData<(*const UnsafeCell<()>, PhantomPinned)>>`
+ --> $RUST/core/src/cell.rs
+  |
+  | pub struct UnsafeCell<T: ?Sized> {
+  |            ^^^^^^^^^^
+note: required because it appears within the type `objc_object`
+ --> $WORKSPACE/crates/objc-sys/src/object.rs
+  |
+  | pub struct objc_object {
+  |            ^^^^^^^^^^^
+note: required because it appears within the type `AnyObject`
+ --> $WORKSPACE/crates/objc2/src/runtime/mod.rs
+  |
+  | pub struct AnyObject(ffi::objc_object);
+  |            ^^^^^^^^^
+note: required because it appears within the type `NSObject`
+ --> $WORKSPACE/crates/objc2/src/runtime/nsobject.rs
+  |
+  | pub struct NSObject {
+  |            ^^^^^^^^
+  = note: required for `dyn NSObjectProtocol + Send + Sync` to implement `ImplementedBy<NSObject>`
+note: required by a bound in `ProtocolObject::<P>::from_ref`
+ --> $WORKSPACE/crates/objc2/src/runtime/protocol_object.rs
+  |
+  |     pub fn from_ref<T: ?Sized + Message>(obj: &T) -> &Self
+  |            -------- required by a bound in this associated function
+  |     where
+  |         P: ImplementedBy<T>,
+  |            ^^^^^^^^^^^^^^^^ required by this bound in `ProtocolObject::<P>::from_ref`
+
+error[E0277]: the trait bound `NSObject: NSCopying` is not satisfied
+ --> ui/protocol_object_only_protocols.rs
+  |
+  |     let _: &ProtocolObject<dyn NSCopying> = ProtocolObject::from_ref(&*obj);
+  |                                             ------------------------ ^^^^^ the trait `NSCopying` is not implemented for `NSObject`
+  |                                             |
+  |                                             required by a bound introduced by this call
+  |
+  = help: the following other types implement trait `NSCopying`:
+            ProtocolObject<T>
+            __RcTestObject
+            NSCollectionLayoutSection
+            NSCollectionLayoutGroupCustomItem
+            NSArray<ObjectType>
+            NSMutableArray<ObjectType>
+            NSDictionary<KeyType, ObjectType>
+            NSSet<ObjectType>
+          and $N others
+  = note: required for `dyn NSCopying` to implement `ImplementedBy<NSObject>`
+note: required by a bound in `ProtocolObject::<P>::from_ref`
+ --> $WORKSPACE/crates/objc2/src/runtime/protocol_object.rs
+  |
+  |     pub fn from_ref<T: ?Sized + Message>(obj: &T) -> &Self
+  |            -------- required by a bound in this associated function
+  |     where
+  |         P: ImplementedBy<T>,
+  |            ^^^^^^^^^^^^^^^^ required by this bound in `ProtocolObject::<P>::from_ref`
+
+error[E0277]: the trait bound `dyn NSCopying + Send: ImplementedBy<NSObject>` is not satisfied
+ --> ui/protocol_object_only_protocols.rs
+  |
+  |     let _: &ProtocolObject<dyn NSCopying + Send> = ProtocolObject::from_ref(&*obj);
+  |                                                    ------------------------ ^^^^^ the trait `ImplementedBy<NSObject>` is not implemented for `dyn NSCopying + Send`
+  |                                                    |
+  |                                                    required by a bound introduced by this call
+  |
+  = help: the following other types implement trait `ImplementedBy<T>`:
+            (dyn NSObjectProtocol + 'static)
+            (dyn NSObjectProtocol + Send + 'static)
+            (dyn NSObjectProtocol + Sync + 'static)
+            (dyn NSObjectProtocol + Send + Sync + 'static)
+            (dyn NSAccessibilityColor + 'static)
+            (dyn NSAccessibilityCustomRotorItemSearchDelegate + 'static)
+            (dyn NSAccessibilityElementProtocol + 'static)
+            (dyn NSAccessibilityGroup + 'static)
+          and $N others
+note: required by a bound in `ProtocolObject::<P>::from_ref`
+ --> $WORKSPACE/crates/objc2/src/runtime/protocol_object.rs
+  |
+  |     pub fn from_ref<T: ?Sized + Message>(obj: &T) -> &Self
+  |            -------- required by a bound in this associated function
+  |     where
+  |         P: ImplementedBy<T>,
+  |            ^^^^^^^^^^^^^^^^ required by this bound in `ProtocolObject::<P>::from_ref`