diff --git a/reactos/drivers/storage/class/disk/disk.c b/reactos/drivers/storage/class/disk/disk.c
index f042031c467..0563702fd40 100644
--- a/reactos/drivers/storage/class/disk/disk.c
+++ b/reactos/drivers/storage/class/disk/disk.c
@@ -4283,7 +4283,7 @@ diskMatched:
     DeviceExtension->DiskGeometry->Geometry.SectorsPerTrack = sectorsPerTrack;
     DeviceExtension->DiskGeometry->Geometry.TracksPerCylinder = tracksPerCylinder;
     DeviceExtension->DiskGeometry->Geometry.Cylinders.QuadPart = (LONGLONG)cylinders;
-    DeviceExtension->DiskGeometry->DiskSize.QuadPart = cylinders * tracksPerCylinder * sectorsPerTrack *
+    DeviceExtension->DiskGeometry->DiskSize.QuadPart = (LONGLONG)cylinders * tracksPerCylinder * sectorsPerTrack *
                                                        DeviceExtension->DiskGeometry->Geometry.BytesPerSector;
 
     DebugPrint((3,