diff --git a/src/backend/executor/execTuples.c b/src/backend/executor/execTuples.c
index 2c2712ceac..5a2db83987 100644
--- a/src/backend/executor/execTuples.c
+++ b/src/backend/executor/execTuples.c
@@ -253,8 +253,6 @@ tts_virtual_copyslot(TupleTableSlot *dstslot, TupleTableSlot *srcslot)
 {
 	TupleDesc	srcdesc = srcslot->tts_tupleDescriptor;
 
-	Assert(srcdesc->natts <= dstslot->tts_tupleDescriptor->natts);
-
 	tts_virtual_clear(dstslot);
 
 	slot_getallattrs(srcslot);
diff --git a/src/include/executor/tuptable.h b/src/include/executor/tuptable.h
index 4210d6d838..ce96111865 100644
--- a/src/include/executor/tuptable.h
+++ b/src/include/executor/tuptable.h
@@ -174,7 +174,8 @@ struct TupleTableSlotOps
 
 	/*
 	 * Copy the contents of the source slot into the destination slot's own
-	 * context. Invoked using callback of the destination slot.
+	 * context. Invoked using callback of the destination slot.  'dstslot' and
+	 * 'srcslot' can be assumed to have the same number of attributes.
 	 */
 	void		(*copyslot) (TupleTableSlot *dstslot, TupleTableSlot *srcslot);
 
@@ -477,12 +478,19 @@ ExecCopySlotMinimalTuple(TupleTableSlot *slot)
  *
  * If a source's system attributes are supposed to be accessed in the target
  * slot, the target slot and source slot types need to match.
+ *
+ * Currently, source and target slot's TupleDesc must have the same number of
+ * attributes.  Future work could see this relaxed to allow the source to
+ * contain additional attributes and have the code here only copy over the
+ * leading attributes.
  */
 static inline TupleTableSlot *
 ExecCopySlot(TupleTableSlot *dstslot, TupleTableSlot *srcslot)
 {
 	Assert(!TTS_EMPTY(srcslot));
 	Assert(srcslot != dstslot);
+	Assert(dstslot->tts_tupleDescriptor->natts ==
+		   srcslot->tts_tupleDescriptor->natts);
 
 	dstslot->tts_ops->copyslot(dstslot, srcslot);