diff --git a/block/iscsi.c b/block/iscsi.c
index 9beb06d498..ead2bd5aa7 100644
--- a/block/iscsi.c
+++ b/block/iscsi.c
@@ -734,7 +734,7 @@ retry:
         goto out_unlock;
     }
 
-    *pnum = lbasd->num_blocks * iscsilun->block_size;
+    *pnum = (int64_t) lbasd->num_blocks * iscsilun->block_size;
 
     if (lbasd->provisioning == SCSI_PROVISIONING_TYPE_DEALLOCATED ||
         lbasd->provisioning == SCSI_PROVISIONING_TYPE_ANCHORED) {