1 files changed, 2 insertions, 0 deletions
diff --git a/include/ctype.h b/include/ctype.h
index 8ceaa9f9..8f0d1687 100644
--- a/include/ctype.h
+++ b/include/ctype.h
@@ -5,6 +5,8 @@
 extern "C" {
 #endif
 
+#include <features.h>
+
 int   isalnum(int);
 int   isalpha(int);
 int   isblank(int);