diff --git a/folly/python/test/iobuf.py b/folly/python/test/iobuf.py
index ffc9f51290a..1363b5b5271 100644
--- a/folly/python/test/iobuf.py
+++ b/folly/python/test/iobuf.py
@@ -47,6 +47,7 @@ def test_chain(self) -> None:
         self.assertEqual(len(chain), len(control[0]))
         self.assertEqual(chain.chain_size(), sum(len(x) for x in control))
         self.assertEqual(chain.chain_count(), len(control))
+        # pyre-fixme[6]: For 1st argument expected `Buffer` but got `Optional[IOBuf]`.
         self.assertEqual(memoryview(chain.next), control[1])
         self.assertEqual(b"".join(chain), b"".join(control))
 
@@ -59,6 +60,7 @@ def test_cyclic_chain(self) -> None:
         self.assertEqual(len(chain), len(control[0]))
         self.assertEqual(chain.chain_size(), sum(len(x) for x in control))
         self.assertEqual(chain.chain_count(), len(control))
+        # pyre-fixme[6]: For 1st argument expected `Buffer` but got `Optional[IOBuf]`.
         self.assertEqual(memoryview(chain.next), control[1])
         self.assertEqual(b"".join(chain), b"".join(control))
 
@@ -74,6 +76,7 @@ def test_hash(self) -> None:
     def test_empty(self) -> None:
         x = b""
         xb = IOBuf(x)
+        # pyre-fixme[6]: For 1st argument expected `Buffer` but got `IOBuf`.
         self.assertEqual(memoryview(xb), x)
         self.assertEqual(bytes(xb), x)
         self.assertFalse(xb)