diff --git a/Lib/test/test_imaplib.py b/Lib/test/test_imaplib.py
index 6b44490..b97989f 100644
--- a/Lib/test/test_imaplib.py
+++ b/Lib/test/test_imaplib.py
@@ -208,6 +208,8 @@
             self.server.logout()
 
     def test_logincapa(self):
+        for cap in self.server.capabilities:
+            self.assertIsInstance(cap, str)
         self.assertTrue('LOGINDISABLED' in self.server.capabilities)
         self.assertTrue('AUTH=ANONYMOUS' in self.server.capabilities)
         rs = self.server.login(self.username, self.password)
@@ -228,6 +230,8 @@
         self.assertEqual(rs[0], 'OK')
 
     def test_logincapa(self):
+        for cap in self.server.capabilities:
+            self.assertIsInstance(cap, str)
         self.assertFalse('LOGINDISABLED' in self.server.capabilities)
 
 
@@ -237,6 +241,8 @@
     imap_class = IMAP4_SSL
 
     def test_logincapa(self):
+        for cap in self.server.capabilities:
+            self.assertIsInstance(cap, str)
         self.assertFalse('LOGINDISABLED' in self.server.capabilities)
         self.assertTrue('AUTH=PLAIN' in self.server.capabilities)