diff --git a/lib/minitest/unit.rb b/lib/minitest/unit.rb
index c7020e71..f19e472d 100644
--- a/lib/minitest/unit.rb
+++ b/lib/minitest/unit.rb
@@ -294,7 +294,7 @@ def UNDEFINED.inspect; "UNDEFINED"; end
     #   assert_operator 5, :<=, 4
 
     def assert_operator o1, op, o2 = UNDEFINED, msg = nil
-      return assert_predicate o1, op, msg if o2 == UNDEFINED
+      return assert_predicate o1, op, msg if UNDEFINED == o2
       msg = message(msg) { "Expected #{mu_pp(o1)} to be #{op} #{mu_pp(o2)}" }
       assert o1.__send__(op, o2), msg
     end
@@ -595,7 +595,7 @@ def refute_nil obj, msg = nil
     #   refute_operator 1, :<, 2 #=> fail
 
     def refute_operator o1, op, o2 = UNDEFINED, msg = nil
-      return refute_predicate o1, op if o2 == UNDEFINED
+      return refute_predicate o1, op, msg if UNDEFINED == o2
       msg = message(msg) { "Expected #{mu_pp(o1)} to not be #{op} #{mu_pp(o2)}"}
       refute o1.__send__(op, o2), msg
     end
diff --git a/test/test_minitest_unit.rb b/test/test_minitest_unit.rb
index 09a8b05c..32a9767f 100755
--- a/test/test_minitest_unit.rb
+++ b/test/test_minitest_unit.rb
@@ -877,6 +877,13 @@ def test_assert_operator
     @tc.assert_operator 2, :>, 1
   end
 
+  def test_assert_operator_bad_object
+    bad = Object.new
+    def bad.==(other) true end
+
+    @tc.assert_operator bad, :equal?, bad
+  end
+
   def test_assert_operator_triggered
     util_assert_triggered "Expected 2 to be < 1." do
       @tc.assert_operator 2, :<, 1
@@ -1358,6 +1365,13 @@ def test_refute_operator
     @tc.refute_operator 2, :<, 1
   end
 
+  def test_refute_operator_bad_object
+    bad = Object.new
+    def bad.==(other) true end
+
+    @tc.refute_operator true, :equal?, bad
+  end
+
   def test_refute_operator_triggered
     util_assert_triggered "Expected 2 to not be > 1." do
       @tc.refute_operator 2, :>, 1