diff --git a/reactos/ntoskrnl/ex/fastinterlck.c b/reactos/ntoskrnl/ex/fastinterlck.c
index 18fd8545cbb..bddc62cd7bf 100644
--- a/reactos/ntoskrnl/ex/fastinterlck.c
+++ b/reactos/ntoskrnl/ex/fastinterlck.c
@@ -88,7 +88,7 @@ ExInterlockedPopEntrySList(IN PSLIST_HEADER ListHead,
 }
 
 ULONG
-NTAPI
+FASTCALL
 ExfInterlockedAddUlong(IN PULONG Addend,
                        IN ULONG Increment,
                        PKSPIN_LOCK Lock)