diff --git a/Lib/test/test_unicode.py b/Lib/test/test_unicode.py
index 0e6cbb6..5db7a9b 100644
--- a/Lib/test/test_unicode.py
+++ b/Lib/test/test_unicode.py
@@ -1231,8 +1231,11 @@ def __repr__(self):
                           0, 1, 2, 3, 4, 5, 6, 7)
 
         # string format spec errors
-        self.assertRaises(ValueError, "{0:-s}".format, '')
-        self.assertRaises(ValueError, format, "", "-")
+        sign_msg = "Sign not allowed in string format specifier"
+        self.assertRaisesRegex(ValueError, sign_msg, "{0:-s}".format, '')
+        self.assertRaisesRegex(ValueError, sign_msg, format, "", "-")
+        space_msg = "Space not allowed in string format specifier"
+        self.assertRaisesRegex(ValueError, space_msg, "{: }".format, '')
         self.assertRaises(ValueError, "{0:=s}".format, '')
 
         # Alternate formatting is not supported