diff --git a/block/dmg.c b/block/dmg.c
index 1cc5426d8c..f98c94dc47 100644
--- a/block/dmg.c
+++ b/block/dmg.c
@@ -161,7 +161,8 @@ static int dmg_open(BlockDriverState *bs, QDict *options, int flags,
         }
 
         if (type == 0x6d697368 && count >= 244) {
-            int new_size, chunk_count;
+            size_t new_size;
+            uint32_t chunk_count;
 
             offset += 4;
             offset += 200;