diff --git a/Lib/test/test_os.py b/Lib/test/test_os.py
index 88b215be49c5caa..50f6b09b1ee4ccc 100644
--- a/Lib/test/test_os.py
+++ b/Lib/test/test_os.py
@@ -4788,6 +4788,13 @@ def test_posix_pty_functions(self):
         son_path = os.ptsname(mother_fd)
         son_fd = os.open(son_path, os.O_RDWR|os.O_NOCTTY)
         self.addCleanup(os.close, son_fd)
+        if sys.platform.startswith('sunos'):
+            # The slave is not a terminal until these STREAMS modules
+            # are pushed onto it.
+            import fcntl
+            I_PUSH = 0x5302
+            fcntl.ioctl(son_fd, I_PUSH, b'ptem\0')
+            fcntl.ioctl(son_fd, I_PUSH, b'ldterm\0')
         self.assertEqual(os.ptsname(mother_fd), os.ttyname(son_fd))
 
     @unittest.skipUnless(hasattr(os, 'spawnl'), "need os.spawnl()")