diff --git a/reactos/lib/uxtheme/msstyles.c b/reactos/lib/uxtheme/msstyles.c
index 9ce1d17155c..90478c9ed11 100644
--- a/reactos/lib/uxtheme/msstyles.c
+++ b/reactos/lib/uxtheme/msstyles.c
@@ -21,6 +21,7 @@
 #include "config.h"
 
 #include <stdarg.h>
+#include <ctype.h>
 
 #include "windef.h"
 #include "winbase.h"
diff --git a/reactos/lib/uxtheme/uxini.c b/reactos/lib/uxtheme/uxini.c
index aaf3b122de6..43864cd92f0 100644
--- a/reactos/lib/uxtheme/uxini.c
+++ b/reactos/lib/uxtheme/uxini.c
@@ -21,6 +21,7 @@
 #include "config.h"
 
 #include <stdarg.h>
+#include <ctype.h>
 
 #include "windef.h"
 #include "winbase.h"