diff --git a/src/allmydata/test/test_storage.py b/src/allmydata/test/test_storage.py
index 47fcf2beb..af4d549bf 100644
--- a/src/allmydata/test/test_storage.py
+++ b/src/allmydata/test/test_storage.py
@@ -2865,7 +2865,7 @@ class MDMFProxies(AsyncTestCase, ShouldFailMixin):
         mr = MDMFSlotReadProxy(self.storage_server, b"si1", 0)
         d = mr.is_sdmf()
         d.addCallback(lambda issdmf:
-            self.assertFalse(issdmf))
+            self.assertTrue(issdmf))
         return d