diff --git a/lib/camping/mab.rb b/lib/camping/mab.rb
index c431d8a..1c70a8e 100644
--- a/lib/camping/mab.rb
+++ b/lib/camping/mab.rb
@@ -14,7 +14,7 @@ class Mab < Markaby::Builder
     include Views
     def tag!(*g,&b)
       h=g[-1]
-      [:href,:action,:src].map{|a|(h[a]=self/h[a])rescue 0}
+      [:href,:action,:src].map{|a|(h[a]&&=self/h[a])rescue 0}
       super
     end
   end