diff --git a/lib/active_model/serializer/lint.rb b/lib/active_model/serializer/lint.rb
index daa21dca9..3552168e2 100644
--- a/lib/active_model/serializer/lint.rb
+++ b/lib/active_model/serializer/lint.rb
@@ -36,16 +36,10 @@ def test_serializable_hash
     def test_read_attribute_for_serialization
       assert_respond_to resource, :read_attribute_for_serialization, 'The resource should respond to read_attribute_for_serialization'
       actual_arity = resource.method(:read_attribute_for_serialization).arity
-      if defined?(::Rubinius)
-        #  1 for def read_attribute_for_serialization(name); end
-        # -2 for alias :read_attribute_for_serialization :send for rbx because :shrug:
-        assert_includes [1, -2], actual_arity, "expected #{actual_arity.inspect} to be 1 or -2"
-      else
-        # using absolute value since arity is:
-        #  1 for def read_attribute_for_serialization(name); end
-        # -1 for alias :read_attribute_for_serialization :send
-        assert_includes [1, -1], actual_arity, "expected #{actual_arity.inspect} to be 1 or -1"
-      end
+      # using absolute value since arity is:
+      #  1 for def read_attribute_for_serialization(name); end
+      # -1 for alias :read_attribute_for_serialization :send
+      assert_equal 1, actual_arity.abs, "expected #{actual_arity.inspect}.abs to be 1 or -1"
     end
 
     # Passes if the object responds to <tt>as_json</tt> and if it takes
@@ -85,8 +79,7 @@ def test_to_json
     def test_cache_key
       assert_respond_to resource, :cache_key
       actual_arity = resource.method(:cache_key).arity
-      assert_includes [-1, 0], actual_arity,
-        "expected #{actual_arity.inspect} to be 0 or -1"
+      assert_includes [-1, 0], actual_arity, "expected #{actual_arity.inspect} to be 0 or -1"
     end
 
     # Passes if the object responds to <tt>updated_at</tt> and if it takes no