diff --git a/Lib/test/test__colorize.py b/Lib/test/test__colorize.py
index ff15d83cb078fe..1959773c4967cd 100644
--- a/Lib/test/test__colorize.py
+++ b/Lib/test/test__colorize.py
@@ -44,11 +44,16 @@ def check(env, fallback, expected):
                 check({'TERM': ''}, fallback, fallback)
                 check({'FORCE_COLOR': '1'}, fallback, True)
                 check({'FORCE_COLOR': '0'}, fallback, True)
+                check({'FORCE_COLOR': ''}, fallback, fallback)
                 check({'NO_COLOR': '1'}, fallback, False)
                 check({'NO_COLOR': '0'}, fallback, False)
+                check({'NO_COLOR': ''}, fallback, fallback)
 
             check({'TERM': 'dumb', 'FORCE_COLOR': '1'}, False, True)
             check({'FORCE_COLOR': '1', 'NO_COLOR': '1'}, True, False)
+            check({'FORCE_COLOR': '1', 'NO_COLOR': ''}, True, True)
+            check({'FORCE_COLOR': '', 'NO_COLOR': '1'}, True, False)
+            check({'FORCE_COLOR': '', 'NO_COLOR': ''}, True, True)
 
             for ignore_environment in False, True:
                 # Simulate running with or without `-E`.
@@ -64,7 +69,9 @@ def check(env, fallback, expected):
 
                     check({'TERM': 'dumb', 'PYTHON_COLORS': '1'}, False, not ignore_environment)
                     check({'NO_COLOR': '1', 'PYTHON_COLORS': '1'}, False, not ignore_environment)
+                    check({'NO_COLOR': '', 'PYTHON_COLORS': '1'}, False, not ignore_environment)
                     check({'FORCE_COLOR': '1', 'PYTHON_COLORS': '0'}, True, ignore_environment)
+                    check({'FORCE_COLOR': '', 'PYTHON_COLORS': '0'}, True, ignore_environment)
 
     @unittest.skipUnless(sys.platform == "win32", "requires Windows")
     def test_colorized_detection_checks_on_windows(self):