diff --git a/lib/jsduck/merger.rb b/lib/jsduck/merger.rb
index 171b775c60505eae4318bcdff4645f43a9b8a673..bfcf5b484526f288bae529452ac6a59d9767a0a8 100644
--- a/lib/jsduck/merger.rb
+++ b/lib/jsduck/merger.rb
@@ -290,14 +290,16 @@ module JsDuck
     def detect_extends(doc_map, code)
       if doc_map[:extends]
         cls = doc_map[:extends].first[:extends]
-        # Ignore extending of the Object class
-        cls == "Object" ? nil : cls
       elsif code[:type] == :assignment && code[:right] && code[:right][:type] == :ext_extend
-        code[:right][:extend].join(".")
+        cls = code[:right][:extend].join(".")
       elsif code[:type] == :ext_define
         # Classes defined with Ext.define will automatically inherit from Ext.Base
-        code[:extend] || "Ext.Base"
+        cls = code[:extend] || "Ext.Base"
+      else
+        cls = nil
       end
+      # Ignore extending of the Object class
+      cls == "Object" ? nil : cls
     end
 
     def detect_default(tagname, doc_map, code)
diff --git a/spec/aggregator_classes_spec.rb b/spec/aggregator_classes_spec.rb
index 2e5f8304a555ba153bc48e4eab116ff5057108d4..35f8974abbc69ccfe5d026257cdf223354680c9a 100644
--- a/spec/aggregator_classes_spec.rb
+++ b/spec/aggregator_classes_spec.rb
@@ -548,4 +548,52 @@ describe JsDuck::Aggregator do
       @classes.length.should == 1
     end
   end
+
+
+  shared_examples_for "extending Object" do
+    it "has extends == nil" do
+      @doc[:extends].should == nil
+    end
+  end
+
+  describe "Class explicitly extending Object" do
+    before do
+      @doc = parse(<<-EOS)[0]
+        /**
+         * @class Foo
+         * @extends Object
+         */
+      EOS
+    end
+    it_should_behave_like "extending Object"
+  end
+
+  describe "Ext.define extending Object" do
+    before do
+      @doc = parse(<<-EOS)[0]
+        /** */
+        Ext.define("Foo", {extend: "Object"});
+      EOS
+    end
+    it_should_behave_like "extending Object"
+  end
+
+  describe "Ext.extend extending Object" do
+    before do
+      @doc = parse(<<-EOS)[0]
+        /** */
+        Foo = Ext.extend(Object, { });
+      EOS
+    end
+    it_should_behave_like "extending Object"
+  end
+
+  describe "Explicit class without @extends" do
+    before do
+      @doc = parse(<<-EOS)[0]
+        /** @class Foo */
+      EOS
+    end
+    it_should_behave_like "extending Object"
+  end
 end