diff --git a/lib.py b/lib.py
index 37b72c3..f4e8799 100644
--- a/lib.py
+++ b/lib.py
@@ -83,7 +83,7 @@ def execute(program):
             elif ctx[0] == _ident("%"):
                 return (subs[1][0], subs[1][1]%subs[2][1])
             elif ctx[0] == _ident("!"):
-                return ("number", 0.0 if subs[1] else 1.0)
+                return ("number", 0.0 if _truthy(subs[1]) else 1.0)
             elif ctx[0] == _ident("=="):
                 return ("number", 1.0 if subs[1] == subs[2] else 0.0)
             elif ctx[0] == _ident("="):