diff --git a/Cargo.lock b/Cargo.lock
index b1cdddedfb..a3208084c6 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -3031,6 +3031,9 @@ name = "smallvec"
 version = "1.10.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "a507befe795404456341dfab10cef66ead4c041f62b8b11bbb92bffe5d0953e0"
+dependencies = [
+ "serde",
+]
 
 [[package]]
 name = "socket2"
diff --git a/sqlx-postgres/Cargo.toml b/sqlx-postgres/Cargo.toml
index 0fd05720c5..b157445e39 100644
--- a/sqlx-postgres/Cargo.toml
+++ b/sqlx-postgres/Cargo.toml
@@ -58,7 +58,7 @@ log = "0.4.17"
 memchr = { version = "2.4.1", default-features = false }
 num-bigint = { version = "0.4.3", optional = true }
 once_cell = "1.9.0"
-smallvec = "1.7.0"
+smallvec = { version = "1.7.0", features = ["serde"] }
 stringprep = "0.1.2"
 thiserror = "1.0.35"
 tracing = { version = "0.1.37", features = ["log"] }
diff --git a/sqlx-postgres/src/connection/describe.rs b/sqlx-postgres/src/connection/describe.rs
index 8a5d1a23db..189ae3389b 100644
--- a/sqlx-postgres/src/connection/describe.rs
+++ b/sqlx-postgres/src/connection/describe.rs
@@ -10,6 +10,7 @@ use crate::types::Oid;
 use crate::HashMap;
 use crate::{PgArguments, PgColumn, PgConnection, PgTypeInfo};
 use futures_core::future::BoxFuture;
+use smallvec::SmallVec;
 use std::fmt::Write;
 use std::sync::Arc;
 
@@ -447,7 +448,8 @@ WHERE rngtypid = $1
             explain += ")";
         }
 
-        let (Json(explains),): (Json<Vec<Explain>>,) = query_as(&explain).fetch_one(self).await?;
+        let (Json(explains),): (Json<SmallVec<[Explain; 1]>>,) =
+            query_as(&explain).fetch_one(self).await?;
 
         let mut nullables = Vec::new();
 
@@ -460,7 +462,7 @@ WHERE rngtypid = $1
         }) = explains.first()
         {
             nullables.resize(outputs.len(), None);
-            visit_plan(plan, outputs, &mut nullables);
+            visit_plan(&plan, outputs, &mut nullables);
         }
 
         Ok(nullables)