diff --git a/src/runtime/hashmap.go b/src/runtime/hashmap.go
index 9e18192cd8..d549ce4194 100644
--- a/src/runtime/hashmap.go
+++ b/src/runtime/hashmap.go
@@ -790,7 +790,9 @@ next:
 				}
 			}
 			it.bucket = bucket
-			it.bptr = b
+			if it.bptr != b { // avoid unnecessary write barrier; see issue 14921
+				it.bptr = b
+			}
 			it.i = i + 1
 			it.checkBucket = checkBucket
 			return