diff --git a/src/lib.js b/src/lib.js
index 812d09a..55f11f8 100644
--- a/src/lib.js
+++ b/src/lib.js
@@ -267,18 +267,35 @@ export function yDocToProsemirrorJSON (
         }
 
         if (d.attributes) {
-          text.marks = Object.keys(d.attributes).map((type) => {
-            const attrs = d.attributes[type]
-            const mark = {
-              type
-            }
+          let marks = []
+          text.marks = Object.keys(d.attributes).forEach((type) => {
+            let attrs = d.attributes[type]
+            if (Array.isArray(attrs)) {
+              // multiple marks of same type
+              attrs.forEach(singleAttrs => {
+                const mark = {
+                  type
+                }
 
-            if (Object.keys(attrs)) {
-              mark.attrs = attrs
-            }
+                if (Object.keys(singleAttrs)) {
+                  mark.attrs = singleAttrs
+                }
+
+                marks.push(mark)
+              })
+            } else {
+              const mark = {
+                type
+              }
 
-            return mark
+              if (Object.keys(attrs)) {
+                mark.attrs = attrs
+              }
+
+              marks.push(mark)
+            }
           })
+          text.marks = marks
         }
         return text
       })
diff --git a/src/plugins/sync-plugin.js b/src/plugins/sync-plugin.js
index 7051bbd..a1000bf 100644
--- a/src/plugins/sync-plugin.js
+++ b/src/plugins/sync-plugin.js
@@ -473,7 +473,15 @@ const createTextNodesFromYText = (text, schema, mapping, snapshot, prevSnapshot,
       const delta = deltas[i]
       const marks = []
       for (const markName in delta.attributes) {
-        marks.push(schema.mark(markName, delta.attributes[markName]))
+        if (Array.isArray(delta.attributes[markName])) {
+          // multiple marks of same type
+          delta.attributes[markName].forEach(attrs => {
+            marks.push(schema.mark(markName, attrs))
+          })
+        } else {
+          // single mark
+          marks.push(schema.mark(markName, delta.attributes[markName]))
+        }
       }
       nodes.push(schema.text(delta.insert, marks))
     }
@@ -545,6 +553,14 @@ const equalAttrs = (pattrs, yattrs) => {
   return eq
 }
 
+const containsEqualMark = (pattrs, yattrs) => {
+  if (Array.isArray(yattrs)) {
+    return !!yattrs.find(el => equalAttrs(pattrs, el))
+  } else {
+    return equalAttrs(pattrs, yattrs)
+  }
+}
+
 /**
  * @typedef {Array<Array<PModel.Node>|PModel.Node>} NormalizedPNodeContent
  */
@@ -572,13 +588,25 @@ const normalizePNodeContent = pnode => {
   return res
 }
 
+const countYTextMarks = (yattrs) => {
+  let count = 0
+  object.forEach(yattrs, (val) => {
+    if (Array.isArray(val)) {
+      count += val.length
+    } else {
+      count++
+    }
+  })
+  return count
+}
+
 /**
  * @param {Y.XmlText} ytext
  * @param {Array<any>} ptexts
  */
 const equalYTextPText = (ytext, ptexts) => {
   const delta = ytext.toDelta()
-  return delta.length === ptexts.length && delta.every((d, i) => d.insert === /** @type {any} */ (ptexts[i]).text && object.keys(d.attributes || {}).length === ptexts[i].marks.length && ptexts[i].marks.every(mark => equalAttrs(d.attributes[mark.type.name] || {}, mark.attrs)))
+  return delta.length === ptexts.length && delta.every((d, i) => d.insert === /** @type {any} */ (ptexts[i]).text && countYTextMarks(d.attributes || {}) === ptexts[i].marks.length && ptexts[i].marks.every(mark => containsEqualMark(d.attributes[mark.type.name] || {}, mark.attrs)))
 }
 
 /**
@@ -682,7 +710,16 @@ const marksToAttributes = marks => {
   const pattrs = {}
   marks.forEach(mark => {
     if (mark.type.name !== 'ychange') {
-      pattrs[mark.type.name] = mark.attrs
+      if (pattrs[mark.type.name] && Array.isArray(pattrs[mark.type.name])) {
+        // already has multiple marks of same type
+        pattrs[mark.type.name].push(mark.attrs)
+      } else if (pattrs[mark.type.name]) {
+        // already has mark of same type, change to array
+        pattrs[mark.type.name] = [pattrs[mark.type.name], mark.attrs]
+      } else {
+        // first mark of this type
+        pattrs[mark.type.name] = mark.attrs
+      }
     }
   })
   return pattrs
diff --git a/test/complexSchema.js b/test/complexSchema.js
index 013190d..c8cda86 100644
--- a/test/complexSchema.js
+++ b/test/complexSchema.js
@@ -157,6 +157,7 @@ export const nodes = {
 const emDOM = ['em', 0]
 const strongDOM = ['strong', 0]
 const codeDOM = ['code', 0]
+const commentDOM = ['span', 0]
 
 // :: Object [Specs](#model.MarkSpec) for the marks in the schema.
 export const marks = {
@@ -223,6 +224,16 @@ export const marks = {
       return codeDOM
     }
   },
+  comment: {
+    attrs: {
+      id: { default: null }
+    },
+    exclude: '', // allow multiple "comments" marks to overlap
+    parseDOM: [{ tag: 'span' }],
+    toDOM () {
+      return commentDOM
+    }
+  },
   ychange: {
     attrs: {
       user: { default: null },
diff --git a/test/y-prosemirror.test.js b/test/y-prosemirror.test.js
index a26fbf6..92971e5 100644
--- a/test/y-prosemirror.test.js
+++ b/test/y-prosemirror.test.js
@@ -26,6 +26,36 @@ export const testDocTransformation = tc => {
   t.compare(stateJSON, backandforth)
 }
 
+/**
+ * @param {t.TestCase} tc
+ */
+export const testDuplicateMarks = tc => {
+  const ydoc = new Y.Doc()
+  const type = ydoc.getXmlFragment('prosemirror')
+  const view = createNewComplexProsemirrorView(ydoc)
+  t.assert(type.toString() === '', 'should only sync after first change')
+
+  view.dispatch(
+    view.state.tr.setNodeMarkup(0, undefined, {
+      checked: true
+    })
+  )
+
+  const marks = [complexSchema.mark('comment', { id: 0 }), complexSchema.mark('comment', { id: 1 })]
+  view.dispatch(view.state.tr.insert(view.state.doc.content.size - 1, /** @type {any} */ complexSchema.text('hello world', marks)))
+  const stateJSON = view.state.doc.toJSON()
+
+  // test if transforming back and forth from Yjs doc works
+  const backandforth = yDocToProsemirrorJSON(prosemirrorJSONToYDoc(/** @type {any} */ (complexSchema), stateJSON))
+
+  // TODO: I think the duplicate marks work, but I think this fails because
+  // there is a yChange on stateJSON.content[1] (and not on backandforth)
+  t.compare(stateJSON, backandforth)
+
+  // TODO: create a toString test, this currently fails because YXmlText breaks
+  // t.compareStrings(type.toString(), '<custom checked="true"></custom><paragraph></paragraph>')
+}
+
 /**
  * @param {t.TestCase} tc
  */