diff --git a/kitty/keys.c b/kitty/keys.c
index eae62eb5a..1a71a225f 100644
--- a/kitty/keys.c
+++ b/kitty/keys.c
@@ -78,7 +78,11 @@ send_key_to_child(Window *w, int key, int mods, int action) {
 
 static inline bool
 is_ascii_control_char(char c) {
+#if CHAR_MIN == 0
+    return (c <= 31) || c == 127;
+#else
     return (0 <= c && c <= 31) || c == 127;
+#endif
 }
 
 void