diff --git a/reactos/tools/widl/widl_ros.diff b/reactos/tools/widl/widl_ros.diff
index 84aff9839cd..fa681a0feb0 100644
--- a/reactos/tools/widl/widl_ros.diff
+++ b/reactos/tools/widl/widl_ros.diff
@@ -110,6 +110,16 @@ Index: widltypes.h
  #include <stdarg.h>
  #include "guiddef.h"
  #include "wine/rpcfc.h"
+@@ -38,7 +38,9 @@
+ typedef GUID UUID;
+ #endif
+ 
++#ifndef TRUE
+ #define TRUE 1
++#endif
+ #define FALSE 0
+ 
+ typedef struct _attr_t attr_t;
 Index: write_msft.c
 ===================================================================
 --- write_msft.c	(revision 32187)
diff --git a/reactos/tools/widl/widltypes.h b/reactos/tools/widl/widltypes.h
index af602f40c8a..6be4d86b731 100644
--- a/reactos/tools/widl/widltypes.h
+++ b/reactos/tools/widl/widltypes.h
@@ -38,7 +38,9 @@
 typedef GUID UUID;
 #endif
 
+#ifndef TRUE
 #define TRUE 1
+#endif
 #define FALSE 0
 
 typedef struct _attr_t attr_t;