diff --git a/functions/api/github-auth-callback.ts b/functions/api/github-auth-callback.ts
index 034c73211..ce9104fb9 100644
--- a/functions/api/github-auth-callback.ts
+++ b/functions/api/github-auth-callback.ts
@@ -60,6 +60,7 @@ export const onRequest: PagesFunction<{
 		const response = await fetch('https://github.com/login/oauth/access_token', {
 			method: 'POST',
 			body: JSON.stringify({ client_id: env.GITHUB_OAUTH_ID, client_secret: env.GITHUB_OAUTH_SECRET, code }),
+			headers: { 'content-type': 'application/json' },
 		});
 		return response.json().then((result) => createResponse(response.status, result));
 	} catch (e) {
diff --git a/functions/api/gitlab-auth-callback.ts b/functions/api/gitlab-auth-callback.ts
index 39befcf15..bf43a2505 100644
--- a/functions/api/gitlab-auth-callback.ts
+++ b/functions/api/gitlab-auth-callback.ts
@@ -68,6 +68,7 @@ export const onRequest: PagesFunction<{
 				redirect_uri: AUTH_REDIRECT_URI,
 				grant_type: 'authorization_code',
 			}),
+			headers: { 'content-type': 'application/json' },
 		});
 		return response.json().then((result) => createResponse(response.status, result));
 	} catch (e) {