diff --git a/src/pen.js b/src/pen.js
index dd4735d..1c8d621 100644
--- a/src/pen.js
+++ b/src/pen.js
@@ -135,7 +135,7 @@
   }
 
   function commandWrap(ctx, tag, value) {
-    value = '<' + tag + '>' + value + '</' + tag + '>';
+    value = '<' + tag + '>' + (value||'') + '</' + tag + '>';
     return commandOverall(ctx, 'insertHTML', value);
   }