diff --git a/pyk/src/pyk/k2lean4/model.py b/pyk/src/pyk/k2lean4/model.py
index dcff434b92..704e05315f 100644
--- a/pyk/src/pyk/k2lean4/model.py
+++ b/pyk/src/pyk/k2lean4/model.py
@@ -9,7 +9,7 @@
     from collections.abc import Iterable
     from typing import Final
 
-_LEAN_KEYWORDS: Final = {'ite', 'end', 'where'}  # Words that cannot be a the name of a declaration
+_LEAN_WORDS: Final = {'ite', 'end', 'where'}  # Words that cannot be a the name of a declaration
 
 
 def indent(text: str, n: int) -> str:
@@ -24,10 +24,10 @@ def mask_name(name: str, mask: str | None) -> str:
     """Append `mask` to `name` if `name` is in `_LEAN_KEYWORDS`."""
     if name == '':
         return ''
-    elif name not in _LEAN_KEYWORDS:
+    elif name not in _LEAN_WORDS:
         return name
     else:
-        return f'{name}{mask}' if mask is not None and is not '' else f'{name}Mask'
+        return f'{name}{mask}' if mask is not None and mask != '' else f'{name}Mask'
 
 
 @final