diff --git a/reactos/include/ddk/ntifs.h b/reactos/include/ddk/ntifs.h
index 62d29154029..ae1e5025ecf 100644
--- a/reactos/include/ddk/ntifs.h
+++ b/reactos/include/ddk/ntifs.h
@@ -4513,7 +4513,7 @@ BOOLEAN
 NTAPI
 MmSetAddressRangeModified (
     IN PVOID    Address,
-    IN ULONG    Length
+    IN SIZE_T    Length
 );
 
 NTKERNELAPI