diff --git a/lib/std/ascii.zig b/lib/std/ascii.zig
index 4a4564d3d79d4334281195aaa4a4fff559241319..663f7df94f8c181b7a1f1872e07eab7410c700fe 100644
--- a/lib/std/ascii.zig
+++ b/lib/std/ascii.zig
@@ -232,7 +232,7 @@ pub fn isAlpha(c: u8) bool {
 }
 
 pub fn isCntrl(c: u8) bool {
-    return c < 0x20 or c == 127; //DEL
+    return c <= control_code.us or c == control_code.del;
 }
 
 pub fn isDigit(c: u8) bool {