diff --git a/tornado/testing.py b/tornado/testing.py
index f92abab3..b7d2881e 100644
--- a/tornado/testing.py
+++ b/tornado/testing.py
@@ -377,6 +377,11 @@ def gen_test(f):
     return wrapper
 
 
+# Without this attribute, nosetests will try to run gen_test as a test
+# anywhere it is imported.
+gen_test.__test__ = False
+
+
 class LogTrapTestCase(unittest.TestCase):
     """A test case that captures and discards all logging output
     if the test passes.