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
diff --git a/spec/cancan/model_adapters/active_record_adapter_spec.rb b/spec/cancan/model_adapters/active_record_adapter_spec.rb
index ae83a89..2f1b7af 100644
--- a/spec/cancan/model_adapters/active_record_adapter_spec.rb
+++ b/spec/cancan/model_adapters/active_record_adapter_spec.rb
@@ -227,6 +227,12 @@ if ENV["MODEL_ADAPTER"].nil? || ENV["MODEL_ADAPTER"] == "active_record"
       @ability.model_adapter(Article, :read).joins.should == [:project]
     end
 
+    it "should merge nested and non-nested joins" do
+      @ability.can :read, Article, :project => { :blocked => false }
+      @ability.can :read, Article, :project => { :comments => { :spam => true } }
+      @ability.model_adapter(Article, :read).joins.should == [{:project=>[:comments]}]
+    end
+
     it "should restrict articles given a MetaWhere condition" do
       @ability.can :read, Article, :priority.lt => 2
       article1 = Article.create!(:priority => 1)