diff --git a/lib/rdoc/code_object/class_module.rb b/lib/rdoc/code_object/class_module.rb
index 98c486418a..f9af6f309e 100644
--- a/lib/rdoc/code_object/class_module.rb
+++ b/lib/rdoc/code_object/class_module.rb
@@ -221,6 +221,7 @@ def complete min_visibility
     remove_nodoc_children
     embed_mixins
     update_includes
+    update_extends
     remove_invisible min_visibility
   end
 
diff --git a/test/rdoc/test_rdoc_class_module.rb b/test/rdoc/test_rdoc_class_module.rb
index 59e03e2faa..7506d04f3c 100644
--- a/test/rdoc/test_rdoc_class_module.rb
+++ b/test/rdoc/test_rdoc_class_module.rb
@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 require_relative 'xref_test_case'
 
-class TestRDocClassModule < XrefTestCase
+class RDocClassModuleTest < XrefTestCase
 
   def test_add_comment
     tl1 = @store.add_file 'one.rb'
@@ -1548,7 +1548,7 @@ def test_fully_qualified_nesting_namespaces
     assert_equal ["A", "A::B", "A::B::C"], cm3.fully_qualified_nesting_namespaces
   end
 
-  class TestRDocClassModuleMixins < XrefTestCase
+  class RDocClassModuleMixinsTest < XrefTestCase
     def setup
       super
 
@@ -1597,7 +1597,19 @@ def setup
       @klass.add_extend(RDoc::Include.new("Extmod", nil))
 
       @klass.add_include(RDoc::Include.new("ExternalInclude", nil))
+      # Test duplicationg removal
+      @klass.add_include(RDoc::Include.new("ExternalInclude", nil))
+
       @klass.add_extend(RDoc::Include.new("ExternalExtend", nil))
+      # Test duplicationg removal
+      @klass.add_extend(RDoc::Include.new("ExternalExtend", nil))
+    end
+
+    def test_complete_clears_duplicated_includes_and_extends
+      @klass.complete(:protected)
+
+      assert_equal(["Incmod", "ExternalInclude"], @klass.includes.map(&:name))
+      assert_equal(["Extmod", "ExternalExtend"], @klass.extends.map(&:name))
     end
 
     def test_embed_mixin_when_false_does_not_embed_anything