diff --git a/python/google/protobuf/internal/message_test.py b/python/google/protobuf/internal/message_test.py
index 6cf89e8fe8..6b90ddc220 100755
--- a/python/google/protobuf/internal/message_test.py
+++ b/python/google/protobuf/internal/message_test.py
@@ -46,6 +46,7 @@ import pickle
 import pydoc
 import sys
 import unittest
+from unittest import mock
 import warnings
 
 cmp = lambda x, y: (x > y) - (x < y)
@@ -1268,6 +1269,42 @@ class MessageTest(unittest.TestCase):
     self.assertEqual(bool, type(m.repeated_bool[0]))
     self.assertEqual(True, m.repeated_bool[0])
 
+  def testEquality(self, message_module):
+    m = message_module.TestAllTypes()
+    m2 = message_module.TestAllTypes()
+    self.assertEqual(m, m)
+    self.assertEqual(m, m2)
+    self.assertEqual(m2, m)
+
+    different_m = message_module.TestAllTypes()
+    different_m.repeated_float.append(1)
+    self.assertNotEqual(m, different_m)
+    self.assertNotEqual(different_m, m)
+
+    self.assertIsNotNone(m)
+    self.assertIsNotNone(m)
+    self.assertNotEqual(42, m)
+    self.assertNotEqual(m, 42)
+    self.assertNotEqual('foo', m)
+    self.assertNotEqual(m, 'foo')
+
+    self.assertEqual(mock.ANY, m)
+    self.assertEqual(m, mock.ANY)
+
+    class ComparesWithFoo(object):
+
+      def __eq__(self, other):
+        if getattr(other, 'optional_string', 'not_foo') == 'foo':
+          return True
+        return NotImplemented
+
+    m.optional_string = 'foo'
+    self.assertEqual(m, ComparesWithFoo())
+    self.assertEqual(ComparesWithFoo(), m)
+    m.optional_string = 'bar'
+    self.assertNotEqual(m, ComparesWithFoo())
+    self.assertNotEqual(ComparesWithFoo(), m)
+
 
 # Class to test proto2-only features (required, extensions, etc.)
 @testing_refleaks.TestCase
diff --git a/python/google/protobuf/internal/python_message.py b/python/google/protobuf/internal/python_message.py
index d6b36a620a..2bd8bc228a 100755
--- a/python/google/protobuf/internal/python_message.py
+++ b/python/google/protobuf/internal/python_message.py
@@ -987,7 +987,7 @@ def _AddEqualsMethod(message_descriptor, cls):
   def __eq__(self, other):
     if (not isinstance(other, message_mod.Message) or
         other.DESCRIPTOR != self.DESCRIPTOR):
-      return False
+      return NotImplemented
 
     if self is other:
       return True
diff --git a/python/google/protobuf/pyext/message.cc b/python/google/protobuf/pyext/message.cc
index a57b7f295c..0e04fe4e60 100644
--- a/python/google/protobuf/pyext/message.cc
+++ b/python/google/protobuf/pyext/message.cc
@@ -2045,25 +2045,26 @@ static PyObject* RichCompare(CMessage* self, PyObject* other, int opid) {
     Py_INCREF(Py_NotImplemented);
     return Py_NotImplemented;
   }
-  bool equals = true;
-  // If other is not a message, it cannot be equal.
+  // If other is not a message, this implementation doesn't know how to perform
+  // comparisons.
   if (!PyObject_TypeCheck(other, CMessage_Type)) {
+    Py_INCREF(Py_NotImplemented);
+    return Py_NotImplemented;
+  }
+  // Otherwise, we have a CMessage whose message we can inspect.
+  bool equals = true;
+  const google::protobuf::Message* other_message =
+      reinterpret_cast<CMessage*>(other)->message;
+  // If messages don't have the same descriptors, they are not equal.
+  if (equals &&
+      self->message->GetDescriptor() != other_message->GetDescriptor()) {
+    equals = false;
+  }
+  // Check the message contents.
+  if (equals &&
+      !google::protobuf::util::MessageDifferencer::Equals(
+          *self->message, *reinterpret_cast<CMessage*>(other)->message)) {
     equals = false;
-  } else {
-    // Otherwise, we have a CMessage whose message we can inspect.
-    const google::protobuf::Message* other_message =
-        reinterpret_cast<CMessage*>(other)->message;
-    // If messages don't have the same descriptors, they are not equal.
-    if (equals &&
-        self->message->GetDescriptor() != other_message->GetDescriptor()) {
-      equals = false;
-    }
-    // Check the message contents.
-    if (equals &&
-        !google::protobuf::util::MessageDifferencer::Equals(
-            *self->message, *reinterpret_cast<CMessage*>(other)->message)) {
-      equals = false;
-    }
   }
 
   if (equals ^ (opid == Py_EQ)) {