diff --git a/keyserver/src/database/migration-config.js b/keyserver/src/database/migration-config.js
--- a/keyserver/src/database/migration-config.js
+++ b/keyserver/src/database/migration-config.js
@@ -16,7 +16,7 @@
 
 const botViewer = createScriptViewer(bots.commbot.userID);
 
-const migrations: $ReadOnlyMap<number, () => Promise<void>> = new Map([
+const migrations: $ReadOnlyMap<number, () => Promise<mixed>> = new Map([
   [
     0,
     async () => {
@@ -466,6 +466,17 @@
       }
     },
   ],
+  [
+    39,
+    () =>
+      dbQuery(
+        SQL`
+          ALTER TABLE memberships
+            DROP INDEX user,
+            ADD KEY user_role_thread (user, role, thread)
+        `,
+      ),
+  ],
 ]);
 const newDatabaseVersion: number = Math.max(...migrations.keys());
 
diff --git a/keyserver/src/database/setup-db.js b/keyserver/src/database/setup-db.js
--- a/keyserver/src/database/setup-db.js
+++ b/keyserver/src/database/setup-db.js
@@ -306,10 +306,9 @@
         ADD PRIMARY KEY (id);
 
       ALTER TABLE memberships
-        ADD UNIQUE KEY thread_user (thread,user) USING BTREE,
-        ADD KEY role (role) USING BTREE;
-
-      ALTER TABLE memberships ADD INDEX user (user);
+        ADD UNIQUE KEY thread_user (thread, user) USING BTREE,
+        ADD KEY role (role) USING BTREE,
+        ADD KEY user_role_thread (user, role, thread);
 
       ALTER TABLE messages
         ADD PRIMARY KEY (id),