diff --git a/plugins/zyklonb/calc b/plugins/zyklonb/calc
index deea424..1df0596 100755
--- a/plugins/zyklonb/calc
+++ b/plugins/zyklonb/calc
@@ -89,7 +89,7 @@
   (let ([s-len (string-length s)] [with-len (string-length start)])
     (and (>= s-len with-len)
          (string=? (substring s 0 with-len) start)
-         (substring s with-len))))
+         (substring s with-len s-len))))
 
 ; --- Calculator ---------------------------------------------------------------