diff --git a/Lib/test/test_cmath.py b/Lib/test/test_cmath.py
index a96a5780b31b6f..ed25451c4f035d 100644
--- a/Lib/test/test_cmath.py
+++ b/Lib/test/test_cmath.py
@@ -514,6 +514,7 @@ def test_isinf(self):
         self.assertFalse(cmath.isinf(1j))
         self.assertFalse(cmath.isinf(NAN))
         self.assertTrue(cmath.isinf(INF))
+        self.assertTrue(cmath.isinf(-INF))
         self.assertTrue(cmath.isinf(complex(INF, 0)))
         self.assertTrue(cmath.isinf(complex(0, INF)))
         self.assertTrue(cmath.isinf(complex(INF, INF)))