diff --git a/lang/src/lib.asm b/lang/src/lib.asm
index ddb426f..3ae6f59 100644
--- a/lang/src/lib.asm
+++ b/lang/src/lib.asm
@@ -338,7 +338,7 @@ is_alpha:
     jb .false
     ; && c <= 'z') {
     cmp dil, 'z'
-    jbe .true
+    ja .false
     ;   return true;
 .true:
     mov rax, 1