diff --git a/keyserver/src/fetchers/thread-permission-fetchers.js b/keyserver/src/fetchers/thread-permission-fetchers.js
--- a/keyserver/src/fetchers/thread-permission-fetchers.js
+++ b/keyserver/src/fetchers/thread-permission-fetchers.js
@@ -262,6 +262,9 @@
       }
       return results;
     }
+    for (const userID of allCandidates) {
+      results.set(userID, 'non-member');
+    }
     const memberOfContainingThreadQuery = SQL`
       SELECT user, role AS containing_role
       FROM memberships