diff --git a/Klein.php b/Klein.php
index 09eddc9..3526fd7 100644
--- a/Klein.php
+++ b/Klein.php
@@ -33,7 +33,7 @@ class Klein {
             ["{% ifset+:var %}", "if(#1s !== null):"],
             ["{% if+:var %}", "if(#1s !== null && #1s):"],
             ["{% if+:id \(( :var (, :var )*)?\) %}", "if(macro_#1(#2s)):"],
-            ["{% unless+:var %}", "if(!(isset(#1s) && #1s)):"],
+            ["{% unless+:var %}", "if(#1s !== null && #1s)):"],
             ["{% else %}", "else:"],
             ["{% endif %}", "endif;"],
             ["{{ :var }}", "echo #1s;"],