diff --git a/modules/rostests/kmtests/ntos_cc/CcSetFileSizes_drv.c b/modules/rostests/kmtests/ntos_cc/CcSetFileSizes_drv.c
index 241312c12c5..89bc3973cfb 100644
--- a/modules/rostests/kmtests/ntos_cc/CcSetFileSizes_drv.c
+++ b/modules/rostests/kmtests/ntos_cc/CcSetFileSizes_drv.c
@@ -467,7 +467,7 @@ TestIrpHandler(
 
             if (Length > (Fcb->Header.FileSize.QuadPart - Offset.QuadPart))
             {
-                RtlFillMemory(Buffer, Length - Fcb->Header.FileSize.QuadPart, 0xBD);
+                RtlFillMemory(Buffer, Length - (Fcb->Header.FileSize.QuadPart - Offset.QuadPart), 0xBD);
             }
         }
         else