diff --git a/lib/mayaUsd/fileio/primUpdaterManager.cpp b/lib/mayaUsd/fileio/primUpdaterManager.cpp
index 75746c5357..8aa8b75002 100644
--- a/lib/mayaUsd/fileio/primUpdaterManager.cpp
+++ b/lib/mayaUsd/fileio/primUpdaterManager.cpp
@@ -1124,6 +1124,11 @@ bool PrimUpdaterManager::editAsMaya(const Ufe::Path& path, const VtDictionary& u
         return false;
     }
 
+    if (pulledPrim.IsInstanceProxy()) {
+        TF_WARN("Cannot edit a USD instance proxy.");
+        return false;
+    }
+
     MayaUsd::ProgressBarScope progressBar(7, "Converting to Maya Data");
 
     PushPullScope scopeIt(_inPushPull);
@@ -1211,6 +1216,11 @@ bool PrimUpdaterManager::canEditAsMaya(const Ufe::Path& path) const
         return false;
     }
 
+    // USD refuses that we modify point instance proxies, so detect that.
+    if (prim.IsInstanceProxy()) {
+        return false;
+    }
+
     VtDictionary              userArgs;
     UsdMayaPrimUpdaterContext context(UsdTimeCode::Default(), prim.GetStage(), userArgs);
 
diff --git a/test/lib/mayaUsd/fileio/testEditAsMaya.py b/test/lib/mayaUsd/fileio/testEditAsMaya.py
index c4de5de591..9cb80d52d3 100644
--- a/test/lib/mayaUsd/fileio/testEditAsMaya.py
+++ b/test/lib/mayaUsd/fileio/testEditAsMaya.py
@@ -372,8 +372,19 @@ def testIllegalEditAsMaya(self):
         stage = mayaUsd.lib.GetPrim(proxyShapePathStr).GetStage()
         blendShape = stage.DefinePrim('/BlendShape1', 'BlendShape')
         scope = stage.DefinePrim('/Scope1', 'Scope')
-        scope = stage.DefinePrim('/Mesh1', 'Mesh')
-        scope = stage.DefinePrim('/Material1', 'Material')
+        self.assertIsNotNone(scope)
+        mesh = stage.DefinePrim('/Mesh1', 'Mesh')
+        self.assertIsNotNone(mesh)
+        mat = stage.DefinePrim('/Material1', 'Material')
+        self.assertIsNotNone(mat)
+        instanced = stage.DefinePrim('/Instanced', 'Xform')
+        self.assertIsNotNone(instanced)
+        proto = stage.DefinePrim('/Proto', 'Xform')
+        self.assertIsNotNone(proto)
+        protoMesh = stage.DefinePrim('/Proto/Mesh', 'Mesh')
+        self.assertIsNotNone(protoMesh)
+        instanced.GetReferences().AddInternalReference('/Proto')
+        instanced.SetInstanceable(True)
 
         blendShapePathStr = proxyShapePathStr + ',/BlendShape1'
         scopePathStr = proxyShapePathStr + ',/Scope1'
@@ -398,6 +409,10 @@ def testIllegalEditAsMaya(self):
         # capability.
         self.assertFalse(mayaUsd.lib.PrimUpdaterManager.canEditAsMaya(proxyShapePathStr + ',/Material1'))
 
+        # Instance proxies cannot be edited as Maya: it explicitly disables this
+        # capability.
+        self.assertFalse(mayaUsd.lib.PrimUpdaterManager.canEditAsMaya(proxyShapePathStr + ',/Instanced/Proto/Mesh'))
+
     def testSessionLayer(self):
         '''Verify that the edit gets on the sessionLayer instead of the editTarget layer.'''