diff --git a/cpplint.py b/cpplint.py
index 42e3da3..e3b36c6 100755
--- a/cpplint.py
+++ b/cpplint.py
@@ -2530,7 +2530,7 @@
     #   };
     class_decl_match = Match(
         r'^(\s*(?:template\s*<[\w\s<>,:]*>\s*)?'
-        r'(class|struct)\s+(?:[A-Z_]+\s+)*(\w+(?:::\w+)*))'
+        r'(class|struct)\s+(?:[A-Z0-9_]+\s+)*(\w+(?:::\w+)*))'
         r'(.*)$', line)
     if (class_decl_match and
         (not self.stack or self.stack[-1].open_parentheses == 0)):