diff --git a/lib/jekyll/utils.rb b/lib/jekyll/utils.rb
index ca9e6fba..1f0af762 100644
--- a/lib/jekyll/utils.rb
+++ b/lib/jekyll/utils.rb
@@ -302,16 +302,11 @@ module Jekyll
 
     private
     def merge_default_proc(target, overwrite)
-      if default_proc?(target) && default_proc?(overwrite) && target.default_proc.nil?
+      if target.is_a?(Hash) && overwrite.is_a?(Hash) && target.default_proc.nil?
         target.default_proc = overwrite.default_proc
       end
     end
 
-    private
-    def default_proc?(object)
-      object.respond_to?(:default_proc)
-    end
-
     private
     def duplicate_frozen_values(target)
       target.each do |key, val|