diff --git a/app/services/oauth2.js b/app/services/oauth2.js
index ce7200a..f871311 100644
--- a/app/services/oauth2.js
+++ b/app/services/oauth2.js
@@ -131,7 +131,9 @@ class OAuth2Service extends SiteService {
 
   async processAuthorize (clientID, redirectUri, done) {
     try {
-      const client = await OAuth2Client.findOne({ clientID });
+      const client = await OAuth2Client
+        .findOne({ _id: mongoose.Types.ObjectId(clientID) })
+        .lean();
       if (!client) {
         this.log.alert('OAuth2 client not found', { clientID });
         return done(null, false);