diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index 1ce42ea9702..5fd7f1e1a20 100644
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -2324,6 +2324,17 @@ FreeBulkInsertState(BulkInsertState bistate)
 	pfree(bistate);
 }
 
+/*
+ * ReleaseBulkInsertStatePin - release a buffer currently held in bistate
+ */
+void
+ReleaseBulkInsertStatePin(BulkInsertState bistate)
+{
+	if (bistate->current_buf != InvalidBuffer)
+		ReleaseBuffer(bistate->current_buf);
+	bistate->current_buf = InvalidBuffer;
+}
+
 
 /*
  *	heap_insert		- insert tuple into a heap
diff --git a/src/backend/commands/copy.c b/src/backend/commands/copy.c
index c05e14e26f7..6b199c122f1 100644
--- a/src/backend/commands/copy.c
+++ b/src/backend/commands/copy.c
@@ -2307,6 +2307,7 @@ CopyFrom(CopyState cstate)
 	uint64		processed = 0;
 	bool		useHeapMultiInsert;
 	int			nBufferedTuples = 0;
+	int			prev_leaf_part_index = -1;
 
 #define MAX_BUFFERED_TUPLES 1000
 	HeapTuple  *bufferedTuples = NULL;	/* initialize to silence warning */
@@ -2561,6 +2562,17 @@ CopyFrom(CopyState cstate)
 			Assert(leaf_part_index >= 0 &&
 				   leaf_part_index < cstate->num_partitions);
 
+			/*
+			 * If this tuple is mapped to a partition that is not same as the
+			 * previous one, we'd better make the bulk insert mechanism gets a
+			 * new buffer.
+			 */
+			if (prev_leaf_part_index != leaf_part_index)
+			{
+				ReleaseBulkInsertStatePin(bistate);
+				prev_leaf_part_index = leaf_part_index;
+			}
+
 			/*
 			 * Save the old ResultRelInfo and switch to the one corresponding
 			 * to the selected partition.
diff --git a/src/include/access/heapam.h b/src/include/access/heapam.h
index ee7e05a3ec7..a864f7860d8 100644
--- a/src/include/access/heapam.h
+++ b/src/include/access/heapam.h
@@ -147,6 +147,7 @@ extern void setLastTid(const ItemPointer tid);
 
 extern BulkInsertState GetBulkInsertState(void);
 extern void FreeBulkInsertState(BulkInsertState);
+extern void ReleaseBulkInsertStatePin(BulkInsertState bistate);
 
 extern Oid heap_insert(Relation relation, HeapTuple tup, CommandId cid,
 			int options, BulkInsertState bistate);