diff --git a/pytools/lex.py b/pytools/lex.py
index a47ea459543c8e133fc5cfcf580820dc2be2d6d5..5ca5b1d3a3b2cf11af924eac786417e5090f1b93 100644
--- a/pytools/lex.py
+++ b/pytools/lex.py
@@ -1,7 +1,7 @@
 import re
 
 
-class RuleError:
+class RuleError(RuntimeError):
     def __init__(self, rule):
         self.Rule = rule
 
@@ -9,7 +9,7 @@ class RuleError:
         return repr(self.Rule)
 
 
-class InvalidTokenError:
+class InvalidTokenError(RuntimeError):
     def __init__(self, s, str_index):
         self.string = s
         self.index = str_index