diff --git a/lex.y b/lex.y
index 599c382..4865b8f 100644
--- a/lex.y
+++ b/lex.y
@@ -156,7 +156,7 @@ regex_concat
 
 regex_base
     : '(' regex_list ')'
-        { $$ = '(' + $2 + ')'; }
+        { $$ = '(?:' + $2 + ')'; }
     | SPECIAL_GROUP regex_list ')'
         { $$ = $1 + $2 + ')'; }
     | regex_base '+'