diff --git a/changelogs/unreleased/mm12935.yml b/changelogs/unreleased/mm12935.yml
new file mode 100644
index 00000000000..782586c514e
--- /dev/null
+++ b/changelogs/unreleased/mm12935.yml
@@ -0,0 +1,5 @@
+---
+title: Remove Content-Type override for Mattermost OAuth login
+merge_request:
+author: Harrison Healey
+type: removed
diff --git a/lib/mattermost/session.rb b/lib/mattermost/session.rb
index e2083848a8d..722e3e04d1c 100644
--- a/lib/mattermost/session.rb
+++ b/lib/mattermost/session.rb
@@ -122,7 +122,7 @@ module Mattermost
 
       @oauth_uri = nil
 
-      response = get('/oauth/gitlab/login', follow_redirects: false, format: 'text/html')
+      response = get('/oauth/gitlab/login', follow_redirects: false)
       return unless (300...400) === response.code
 
       redirect_uri = response.headers['location']