diff --git a/cxxheaderparser/lexer.py b/cxxheaderparser/lexer.py
index e3994fd..fab8311 100644
--- a/cxxheaderparser/lexer.py
+++ b/cxxheaderparser/lexer.py
@@ -213,6 +213,7 @@ class PlyLexer:
         "=",
         "'",
         ".",
+        "?",
     ]
 
     #