diff --git a/CHANGES b/CHANGES
index 3546ab6b90..e6e19d106c 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,3 +1,6 @@
+2850.	[bug]		If isc_heap_insert() failed due to memory shortage
+			the heap would have corrupted entries.
+
 2849.	[bug]		Don't treat errors from the xml2 library as fatal.
 			[RT #20945]
 
diff --git a/lib/isc/heap.c b/lib/isc/heap.c
index 91d78c06d4..7f50eac524 100644
--- a/lib/isc/heap.c
+++ b/lib/isc/heap.c
@@ -15,7 +15,7 @@
  * PERFORMANCE OF THIS SOFTWARE.
  */
 
-/* $Id: heap.c,v 1.37 2007/10/19 17:15:53 explorer Exp $ */
+/* $Id: heap.c,v 1.38 2010/02/04 23:22:05 jinmei Exp $ */
 
 /*! \file
  * Heap implementation of priority queues adapted from the following:
@@ -186,15 +186,17 @@ sink_down(isc_heap_t *heap, unsigned int i, void *elt) {
 
 isc_result_t
 isc_heap_insert(isc_heap_t *heap, void *elt) {
-	unsigned int i;
+	unsigned int new_last;
 
 	REQUIRE(VALID_HEAP(heap));
 
-	i = ++heap->last;
-	if (heap->last >= heap->size && !resize(heap))
+	new_last = heap->last + 1;
+	RUNTIME_CHECK(new_last > 0); /* overflow check */
+	if (new_last >= heap->size && !resize(heap))
 		return (ISC_R_NOMEMORY);
+	heap->last = new_last;
 
-	float_up(heap, i, elt);
+	float_up(heap, new_last, elt);
 
 	return (ISC_R_SUCCESS);
 }