diff --git a/block/qcow2.c b/block/qcow2.c
index a9c39bd8170416ad900feefa8331faf90333714d..9637f2ea3a57c5e45f4c5d5652d805774cc3eb08 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -642,7 +642,7 @@ static int get_bits_from_size(size_t size)
 static int preallocate(BlockDriverState *bs)
 {
     BDRVQcowState *s = bs->opaque;
-    uint64_t cluster_offset;
+    uint64_t cluster_offset = 0;
     uint64_t nb_sectors;
     uint64_t offset;
     int num;