diff --git a/ntoskrnl/cc/view.c b/ntoskrnl/cc/view.c
index c59c103a46b..97d675c2b04 100644
--- a/ntoskrnl/cc/view.c
+++ b/ntoskrnl/cc/view.c
@@ -158,7 +158,7 @@ CcRosTraceCacheMap (
 NTSTATUS
 CcRosFlushVacb (
     _In_ PROS_VACB Vacb,
-    _In_ PIO_STATUS_BLOCK Iosb)
+    _Out_opt_ PIO_STATUS_BLOCK Iosb)
 {
     NTSTATUS Status;
     BOOLEAN HaveLock = FALSE;
diff --git a/ntoskrnl/include/internal/cc.h b/ntoskrnl/include/internal/cc.h
index 1986e888f9e..a56118a8558 100644
--- a/ntoskrnl/include/internal/cc.h
+++ b/ntoskrnl/include/internal/cc.h
@@ -310,7 +310,10 @@ CcMdlWriteComplete2(
 );
 
 NTSTATUS
-CcRosFlushVacb(PROS_VACB Vacb, PIO_STATUS_BLOCK Iosb);
+CcRosFlushVacb(
+    _In_ PROS_VACB Vacb,
+    _Out_opt_ PIO_STATUS_BLOCK Iosb
+);
 
 NTSTATUS
 CcRosGetVacb(