diff --git a/.changeset/slow-mirrors-eat.md b/.changeset/slow-mirrors-eat.md
new file mode 100644
index 0000000000..6996a977d0
--- /dev/null
+++ b/.changeset/slow-mirrors-eat.md
@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-auth-backend': patch
+---
+
+Fix GitLab provider setup so that it supports GitLab installations with a path in the URL.
diff --git a/plugins/auth-backend/src/providers/gitlab/provider.ts b/plugins/auth-backend/src/providers/gitlab/provider.ts
index 7f5489d391..31efafa4ee 100644
--- a/plugins/auth-backend/src/providers/gitlab/provider.ts
+++ b/plugins/auth-backend/src/providers/gitlab/provider.ts
@@ -91,6 +91,9 @@ export class GitlabAuthProvider implements OAuthHandlers {
         clientSecret: options.clientSecret,
         callbackURL: options.callbackUrl,
         baseURL: options.baseUrl,
+        authorizationURL: `${options.baseUrl}/oauth/authorize`,
+        tokenURL: `${options.baseUrl}/oauth/token`,
+        profileURL: `${options.baseUrl}/api/v4/user`,
       },
       (
         accessToken: any,