tests/test_core.py | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/tests/test_core.py b/tests/test_core.py
index 2fae7bc..0773f88 100644
--- a/tests/test_core.py
+++ b/tests/test_core.py
@@ -397,12 +397,12 @@ class TestCore(object):
         ]
 
         # Add override magic to make it easier to test a specific file
-        if "S" in os.environ:
-            pass_tests = [os.environ["S"]]
+        if "_S" in os.environ:
+            pass_tests = [os.environ["_S"]]
             _fail_tests = []
-        elif "F" in os.environ:
+        elif "_F" in os.environ:
             pass_tests = []
-            _fail_tests = [(os.environ["F"], SchemaError)]
+            _fail_tests = [(os.environ["_F"], SchemaError)]
 
         for passing_test_file in pass_tests:
             f = self.f(os.path.join("success", passing_test_file))