# UNDF: UNDF-2026-000000283
--- a/src/Simplex/Chat/Library/Commands.hs
+++ b/src/Simplex/Chat/Library/Commands.hs
@@ -2310,8 +2310,9 @@ processChatCommand vr nm = \case
   APIMembersRole groupId memberIds newRole -> withUser $ \user ->
     withGroupLock "memberRole" groupId $ do
       g@(Group gInfo members) <- withFastStore $ \db -> getGroup db vr user groupId
-      when (selfSelected gInfo) $ throwCmdError "can't change role for self"
-      let (invitedMems, currentMems, unchangedMems, maxRole, anyAdmin, anyPending) = selectMembers members
+      let gmIdSet = S.fromList (L.toList memberIds)
+      when (selfSelected gmIdSet gInfo) $ throwCmdError "can't change role for self"
+      let (invitedMems, currentMems, unchangedMems, maxRole, anyAdmin, anyPending) = selectMembers gmIdSet members
       when (length invitedMems + length currentMems + length unchangedMems /= length memberIds) $ throwChatError CEGroupMemberNotFound
       when (length memberIds > 1 && (anyAdmin || newRole >= GRAdmin)) $
         throwCmdError "can't change role of multiple members when admins selected, or new role is admin"
@@ -2326,12 +2327,12 @@ processChatCommand vr nm = \case
       pure $ CRMembersRoleUser {user, groupInfo = gInfo, members = changed1 <> changed2, toRole = newRole} -- same order is not guaranteed
     where
-      selfSelected GroupInfo {membership} = elem (groupMemberId' membership) memberIds
-      selectMembers :: [GroupMember] -> ([GroupMember], [GroupMember], [GroupMember], GroupMemberRole, Bool, Bool)
-      selectMembers = foldr' addMember ([], [], [], GRObserver, False, False)
+      selfSelected gmIdSet GroupInfo {membership} = S.member (groupMemberId' membership) gmIdSet
+      selectMembers :: S.Set GroupMemberId -> [GroupMember] -> ([GroupMember], [GroupMember], [GroupMember], GroupMemberRole, Bool, Bool)
+      selectMembers gmIdSet = foldr' addMember ([], [], [], GRObserver, False, False)
         where
           addMember m@GroupMember {groupMemberId, memberStatus, memberRole} (invited, current, unchanged, maxRole, anyAdmin, anyPending)
-            | groupMemberId `elem` memberIds =
+            | groupMemberId `S.member` gmIdSet =
                 let maxRole' = max maxRole memberRole
                     anyAdmin' = anyAdmin || memberRole >= GRAdmin
                     anyPending' = anyPending || memberPending m