diff --git a/actionpack/lib/action_view/template/resolver.rb b/actionpack/lib/action_view/template/resolver.rb
index 2b9427ace5..a3516c2a45 100644
--- a/actionpack/lib/action_view/template/resolver.rb
+++ b/actionpack/lib/action_view/template/resolver.rb
@@ -239,7 +239,7 @@ module ActionView
 
       exts.each do |ext|
         query << "{"
-        ext.compact.each { |e| query << ".#{e}," }
+        ext.compact.uniq.each { |e| query << ".#{e}," }
         query << "}"
       end