diff --git a/lark/lexer.py b/lark/lexer.py
index 9d4e184..3ab91b4 100644
--- a/lark/lexer.py
+++ b/lark/lexer.py
@@ -4,7 +4,7 @@ import re
 
 from .utils import Str, classify
 from .common import PatternStr, PatternRE, TokenDef
-from .exceptions import UnexpectedCharacters
+from .exceptions import UnexpectedCharacters, LexError
 
 ###{standalone
 class Token(Str):