1 files changed, 2 insertions, 0 deletions

diff --git a/xs_unicode.h b/xs_unicode.h
index a5a1dcb..9663190 100644
--- a/xs_unicode.h
+++ b/xs_unicode.h
@@ -33,6 +33,8 @@
 
 #ifdef XS_IMPLEMENTATION
 
+#include <ctype.h>
+
 #ifndef xs_countof
 #define xs_countof(a) (sizeof((a)) / sizeof((*a)))
 #endif