diff --git a/reactos/tools/widl/Makefile b/reactos/tools/widl/Makefile
index 2716d5384c9..b70896aaa0e 100644
--- a/reactos/tools/widl/Makefile
+++ b/reactos/tools/widl/Makefile
@@ -36,7 +36,8 @@ CLEAN_FILES = *.o $(TARGET)
 
 HOST_CFLAGS = -DYYDEBUG=1 -DINT16=SHORT -D__USE_W32API \
               -I$(LIB_WPP_DIR) -I$(PATH_TO_TOP)/include/wine \
-              -I$(PATH_TO_TOP)/include -I$(PATH_TO_TOP)/w32api/include
+              -I$(PATH_TO_TOP)/include -I$(PATH_TO_TOP)/w32api/include \
+              -Werror -Wall
 
 %.o: %.c
 	$(HOST_CC) $(HOST_CFLAGS) -c $< -o $@
diff --git a/reactos/tools/widl/hash.c b/reactos/tools/widl/hash.c
index 89822cc5388..8ee30982248 100644
--- a/reactos/tools/widl/hash.c
+++ b/reactos/tools/widl/hash.c
@@ -511,7 +511,7 @@ unsigned long lhash_val_of_name_sys( syskind_t skind, LCID lcid, LPCSTR lpStr)
   switch (PRIMARYLANGID(LANGIDFROMLCID(lcid)))
   {
   default:
-    fprintf(stderr, "Unknown lcid %lx, treating as latin-based, please report\n", lcid);
+    fprintf(stderr, "Unknown lcid %lx, treating as latin-based, please report\n", (long)lcid);
     /* .. Fall Through .. */
   case LANG_AFRIKAANS:  case LANG_ALBANIAN:   case LANG_ARMENIAN:
   case LANG_ASSAMESE:   case LANG_AZERI:      case LANG_BASQUE:
diff --git a/reactos/tools/widl/write_msft.c b/reactos/tools/widl/write_msft.c
index 2d36081a3e8..47cc8be54ba 100644
--- a/reactos/tools/widl/write_msft.c
+++ b/reactos/tools/widl/write_msft.c
@@ -33,6 +33,9 @@
 #include <stdio.h>
 #include <ctype.h>
 #include <time.h>
+#ifdef WIN32
+#include <io.h> /* write() */
+#endif /* WIN32 */
 
 #define NONAMELESSUNION
 #define NONAMELESSSTRUCT