diff --git a/commit.c b/commit.c
index 70f12664ce..5d57450de3 100644
--- a/commit.c
+++ b/commit.c
@@ -311,6 +311,8 @@ int parse_commit(struct commit *item)
 	unsigned long size;
 	int ret;
 
+	if (!item)
+		return -1;
 	if (item->object.parsed)
 		return 0;
 	buffer = read_sha1_file(item->object.sha1, &type, &size);