diff -r 90d318d40a83 Lib/test/test_warnings/__init__.py
--- a/Lib/test/test_warnings/__init__.py	Mon Dec 05 18:23:27 2016 +0100
+++ b/Lib/test/test_warnings/__init__.py	Mon Dec 05 23:27:29 2016 +0100
@@ -944,6 +944,26 @@ class CatchWarningTests(BaseTest):
                 self.assertTrue(wmod.filters is not orig_filters)
             self.assertTrue(wmod.filters is orig_filters)
 
+    def test_record_override_showwarning(self):
+        # Issue #28089: It is possible to override warnings.showwarning()
+        # in the catch_warnings(record=True) context manager.
+        text = "This is a warning"
+        wmod = self.module
+        my_log = []
+
+        def my_logger(message, category, filename, lineno, file=None, line=None):
+            nonlocal my_log
+            my_log.append(message)
+
+        with wmod.catch_warnings(module=wmod, record=True) as log:
+            wmod.showwarning = my_logger
+            wmod.warn(text)
+
+        self.assertEqual(len(my_log), 1, my_log)
+        message = my_log[0]
+        self.assertEqual(message.args[0], text)
+        self.assertEqual(log, [])
+
     def test_check_warnings(self):
         # Explicit tests for the test.support convenience wrapper
         wmod = self.module
diff -r 90d318d40a83 Lib/warnings.py
--- a/Lib/warnings.py	Mon Dec 05 18:23:27 2016 +0100
+++ b/Lib/warnings.py	Mon Dec 05 23:27:29 2016 +0100
@@ -447,11 +447,12 @@ class catch_warnings(object):
         self._module._filters_mutated()
         self._showwarning = self._module.showwarning
         self._showwarnmsg = self._module._showwarnmsg
+        self._showwarnmsg_impl = self._module._showwarnmsg
         if self._record:
             log = []
             def showarnmsg(msg):
                 log.append(msg)
-            self._module._showwarnmsg = showarnmsg
+            self._module._showwarnmsg_impl = showarnmsg
             return log
         else:
             return None
@@ -463,6 +464,7 @@ class catch_warnings(object):
         self._module._filters_mutated()
         self._module.showwarning = self._showwarning
         self._module._showwarnmsg = self._showwarnmsg
+        self._module._showwarnmsg_impl = self._showwarnmsg_impl
 
 
 # filters contains a sequence of filter 5-tuples