diff --git a/content/commands.js b/content/commands.js
index c73b11cd..24ac8959 100644
--- a/content/commands.js
+++ b/content/commands.js
@@ -1166,7 +1166,7 @@ function Commands() //{{{
             }
 
             //                               1        2       3    4  5      6
-            var matches = args.match(/^\s*(no|inv)?([a-z]+)([?&!])?(([+-])?=(.*))?/);
+            var matches = args.match(/^\s*(no|inv)?([a-z_]+)([?&!])?(([+-])?=(.*))?/);
             if (!matches)
             {
                 vimperator.echoerr("E518: Unknown option: " + args);