diff --git a/Lib/signal.py b/Lib/signal.py
index c8cd3d4f597ca5..6387e5c35dbaba 100644
--- a/Lib/signal.py
+++ b/Lib/signal.py
@@ -15,7 +15,7 @@
         'Handlers', __name__,
         lambda name: name in ('SIG_DFL', 'SIG_IGN'))
 
-if 'pthread_sigmask' in _globals:
+if 'SIG_BLOCK' in _globals:
     _IntEnum._convert_(
             'Sigmasks', __name__,
             lambda name: name in ('SIG_BLOCK', 'SIG_UNBLOCK', 'SIG_SETMASK'))
diff --git a/Lib/test/test_signal.py b/Lib/test/test_signal.py
index d6cc22558ec4fa..2cad18a69ff7c0 100644
--- a/Lib/test/test_signal.py
+++ b/Lib/test/test_signal.py
@@ -833,6 +833,8 @@ def test_itimer_real(self):
     # Issue 3864, unknown if this affects earlier versions of freebsd also
     @unittest.skipIf(sys.platform in ('netbsd5',) or is_apple_mobile,
         'itimer not reliable (does not mix well with threading) on some BSDs.')
+    @unittest.skipIf(sys.platform == 'cygwin',
+                     "Cygwin doesn't support ITIMER_VIRTUAL")
     def test_itimer_virtual(self):
         self.itimer = signal.ITIMER_VIRTUAL
         signal.signal(signal.SIGVTALRM, self.sig_vtalrm)
@@ -850,6 +852,8 @@ def test_itimer_virtual(self):
         # and the handler should have been called
         self.assertEqual(self.hndl_called, True)
 
+    @unittest.skipIf(sys.platform == 'cygwin',
+                     "Cygwin doesn't support ITIMER_PROF")
     def test_itimer_prof(self):
         self.itimer = signal.ITIMER_PROF
         signal.signal(signal.SIGPROF, self.sig_prof)