diff --git a/src/storage/storage_backend_disk.c b/src/storage/storage_backend_disk.c
index cb6a8d5469..abab1e19d6 100644
--- a/src/storage/storage_backend_disk.c
+++ b/src/storage/storage_backend_disk.c
@@ -560,7 +560,7 @@ virStorageBackendDiskPartBoundaries(virStoragePoolObjPtr pool,
     unsigned long long extraBytes = 0;
     unsigned long long alignedAllocation = allocation;
     virStoragePoolSourceDevicePtr dev = &pool->def->source.devices[0];
-    unsigned long long cylinderSize = dev->geometry.heads *
+    unsigned long long cylinderSize = (unsigned long long)dev->geometry.heads *
                                       dev->geometry.sectors * SECTOR_SIZE;
 
     VIR_DEBUG("find free area: allocation %llu, cyl size %llu", allocation,