diff --git a/changelog.d/8577.misc b/changelog.d/8577.misc
new file mode 100644
index 000000000000..75fe563a0258
--- /dev/null
+++ b/changelog.d/8577.misc
@@ -0,0 +1 @@
+Adjust a protocol-type definition to fit `sqlite3` assertions.
\ No newline at end of file
diff --git a/synapse/storage/database.py b/synapse/storage/database.py
index 763722d6bce6..0217e631085a 100644
--- a/synapse/storage/database.py
+++ b/synapse/storage/database.py
@@ -160,7 +160,7 @@ def __enter__(self) -> "Connection":
         self.conn.__enter__()
         return self
 
-    def __exit__(self, exc_type, exc_value, traceback) -> bool:
+    def __exit__(self, exc_type, exc_value, traceback) -> Optional[bool]:
         return self.conn.__exit__(exc_type, exc_value, traceback)
 
     # Proxy through any unknown lookups to the DB conn class.
diff --git a/synapse/storage/types.py b/synapse/storage/types.py
index 970bb1b9da35..9cadcba18fc0 100644
--- a/synapse/storage/types.py
+++ b/synapse/storage/types.py
@@ -12,7 +12,7 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-from typing import Any, Iterable, Iterator, List, Tuple
+from typing import Any, Iterable, Iterator, List, Optional, Tuple
 
 from typing_extensions import Protocol
 
@@ -65,5 +65,5 @@ def rollback(self, *args, **kwargs) -> None:
     def __enter__(self) -> "Connection":
         ...
 
-    def __exit__(self, exc_type, exc_value, traceback) -> bool:
+    def __exit__(self, exc_type, exc_value, traceback) -> Optional[bool]:
         ...