diff --git a/reactos/tools/unicode/Makefile b/reactos/tools/unicode/Makefile
index a5d9fd921e2..c561c3bbe6c 100644
--- a/reactos/tools/unicode/Makefile
+++ b/reactos/tools/unicode/Makefile
@@ -8,7 +8,7 @@ TARGET_NAME = unicode
 
 TARGET_CFLAGS = -D__USE_W32API -DWINVER=0x501 -DWINE_UNICODE_API= \
                 -Dwchar_t="unsigned short" -D_WCHAR_T_DEFINED \
-                -I$(PATH_TO_TOP)/include/wine
+                -I$(PATH_TO_TOP)/include/wine -Wall -Werror
 
 CODEPAGES = \
 	037 \
diff --git a/reactos/tools/unicode/string.c b/reactos/tools/unicode/string.c
index 9f94aa19280..6d3926f9659 100644
--- a/reactos/tools/unicode/string.c
+++ b/reactos/tools/unicode/string.c
@@ -20,6 +20,7 @@
 
 #include <limits.h>
 #include <stdio.h>
+#include <ctype.h>
 
 #include "wine/unicode.h"