diff --git a/lib/cancan/model_adapters/active_record_adapter.rb b/lib/cancan/model_adapters/active_record_adapter.rb
index f20da17..d7d856f 100644
--- a/lib/cancan/model_adapters/active_record_adapter.rb
+++ b/lib/cancan/model_adapters/active_record_adapter.rb
@@ -145,8 +145,8 @@ module CanCan
       # Takes two hashes and does a deep merge.
       def merge_joins(base, add)
         add.each do |name, nested|
-          if base[name].is_a?(Hash) && !nested.empty?
-            merge_joins(base[name], nested)
+          if base[name].is_a?(Hash)
+            merge_joins(base[name], nested) unless nested.empty?
           else
             base[name] = nested
           end