diff --git a/actionpack/lib/action_view/template/resolver.rb b/actionpack/lib/action_view/template/resolver.rb
index 979be701b2..c66990e1ca 100644
--- a/actionpack/lib/action_view/template/resolver.rb
+++ b/actionpack/lib/action_view/template/resolver.rb
@@ -241,7 +241,7 @@ module ActionView
 
       exts.each do |ext|
         query << "{"
-        ext.compact.each { |e| query << ".#{e}," }
+        ext.compact.uniq.each { |e| query << ".#{e}," }
         query << "}"
       end