diff --git a/changelog.d/20230918_114322_rra_DM_40744.md b/changelog.d/20230918_114322_rra_DM_40744.md
new file mode 100644
index 00000000..e8eef5ec
--- /dev/null
+++ b/changelog.d/20230918_114322_rra_DM_40744.md
@@ -0,0 +1,3 @@
+### Backwards-incompatible changes
+
+- `safir.github.GitHubAppClientFactory` now expects the application ID and installation ID (for `create_installation_client`) to be of type `int`, not `str`. This appears to match what GitHub's API returns, but not what Gidgethub expects. The ID is converted to a string when passing it to Gidgethub.
diff --git a/src/safir/github/_client.py b/src/safir/github/_client.py
index cf64e286..5608add0 100644
--- a/src/safir/github/_client.py
+++ b/src/safir/github/_client.py
@@ -21,10 +21,16 @@ class GitHubAppClientFactory:
         from (e.g. ``lsst-sqre/times-square``).
     http_client
         The httpx client.
+
+    Notes
+    -----
+    Gidgethub treats the application ID and installation ID as strings, but
+    GitHub's API appears to return them as integers. This class expects them
+    to be integers and converts them to strings when calling Gidgethub.
     """
 
     def __init__(
-        self, *, id: str, key: str, name: str, http_client: httpx.AsyncClient
+        self, *, id: int, key: str, name: str, http_client: httpx.AsyncClient
     ) -> None:
         self.app_id = id
         self.app_key = key
@@ -43,7 +49,7 @@ def get_app_jwt(self) -> str:
             The JWT token.
         """
         return gidgethub.apps.get_jwt(
-            app_id=self.app_id, private_key=self.app_key
+            app_id=str(self.app_id), private_key=self.app_key
         )
 
     def _create_client(self, *, oauth_token: str | None = None) -> GitHubAPI:
@@ -72,7 +78,7 @@ def create_app_client(self) -> GitHubAPI:
         return self._create_client(oauth_token=self.get_app_jwt())
 
     async def create_installation_client(
-        self, installation_id: str
+        self, installation_id: int
     ) -> GitHubAPI:
         """Create a client authenticated as an installation of the GitHub App
         for a specific repository or organization.
@@ -93,8 +99,8 @@ async def create_installation_client(
         anon_client = self.create_anonymous_client()
         token_info = await gidgethub.apps.get_installation_access_token(
             anon_client,
-            installation_id=installation_id,
-            app_id=self.app_id,
+            installation_id=str(installation_id),
+            app_id=str(self.app_id),
             private_key=self.app_key,
         )
         return self._create_client(oauth_token=token_info["token"])