diff --git a/block/vmdk.c b/block/vmdk.c
index fd94b8f..1c5e2ef 100644
--- a/block/vmdk.c
+++ b/block/vmdk.c
@@ -523,7 +523,7 @@
     }
     ret = vmdk_add_extent(bs, file, false,
                           le32_to_cpu(header.disk_sectors),
-                          le32_to_cpu(header.l1dir_offset) << 9,
+                          (int64_t)le32_to_cpu(header.l1dir_offset) << 9,
                           0,
                           le32_to_cpu(header.l1dir_size),
                           4096,