diff --git a/liberty.c b/liberty.c
index 6a771be..6f44df0 100644
--- a/liberty.c
+++ b/liberty.c
@@ -2672,6 +2672,12 @@ strncasecmp_ascii (const char *a, const char *b, size_t n)
 	return 0;
 }
 
+static bool
+iscntrl_ascii (int c)
+{
+	return (c >= 0 && c < 32) || c == 0x7f;
+}
+
 static bool
 isalpha_ascii (int c)
 {