diff --git a/reactos/include/ndk/umtypes.h b/reactos/include/ndk/umtypes.h
index e4810967581..6c5a331d75c 100644
--- a/reactos/include/ndk/umtypes.h
+++ b/reactos/include/ndk/umtypes.h
@@ -54,7 +54,7 @@ Author:
 #ifndef _MANAGED
 #if defined(_M_IX86)
 #ifndef FASTCALL
-#define FASTCALL                        _fastcall
+#define FASTCALL                        __fastcall
 #endif
 #else
 #define FASTCALL
@@ -159,8 +159,8 @@ typedef struct _STRING32 {
     USHORT   Length;
     USHORT   MaximumLength;
     ULONG  Buffer;
-} STRING32, *PSTRING32, 
-  UNICODE_STRING32, *PUNICODE_STRING32, 
+} STRING32, *PSTRING32,
+  UNICODE_STRING32, *PUNICODE_STRING32,
   ANSI_STRING32, *PANSI_STRING32;
 
 typedef struct _STRING64 {
@@ -168,7 +168,7 @@ typedef struct _STRING64 {
     USHORT   MaximumLength;
     ULONGLONG  Buffer;
 } STRING64, *PSTRING64,
-  UNICODE_STRING64, *PUNICODE_STRING64, 
+  UNICODE_STRING64, *PUNICODE_STRING64,
   ANSI_STRING64, *PANSI_STRING64;