diff --git a/app/controllers/groups_controller.rb b/app/controllers/groups_controller.rb
index ff14238113e..54906c2d611 100644
--- a/app/controllers/groups_controller.rb
+++ b/app/controllers/groups_controller.rb
@@ -240,20 +240,20 @@ class GroupsController < ApplicationController
     group = Group.find(params[:id])
     group.public_admission ? ensure_logged_in : guardian.ensure_can_edit!(group)
 
-    users =
-      if params[:usernames].present?
-        User.where(username: params[:usernames].split(","))
-      elsif params[:user_ids].present?
-        User.find(params[:user_ids].split(","))
-      elsif params[:user_emails].present?
-        User.with_email(params[:user_emails].split(","))
-      else
-        raise Discourse::InvalidParameters.new(
-          'user_ids or usernames or user_emails must be present'
-        )
-      end
-
-    raise Discourse::NotFound if users.blank?
+    if params[:usernames].present?
+      users = User.where(username: params[:usernames].split(","))
+      raise Discourse::InvalidParameters.new(:usernames) if users.blank?
+    elsif params[:user_ids].present?
+      users = User.where(id: params[:user_ids].split(","))
+      raise Discourse::InvalidParameters.new(:user_ids) if users.blank?
+    elsif params[:user_emails].present?
+      users = User.with_email(params[:user_emails].split(","))
+      raise Discourse::InvalidParameters.new(:user_emails) if users.blank?
+    else
+      raise Discourse::InvalidParameters.new(
+        'user_ids or usernames or user_emails must be present'
+      )
+    end
 
     if group.public_admission
       if !guardian.can_log_group_changes?(group) && current_user != users.first
diff --git a/spec/requests/groups_controller_spec.rb b/spec/requests/groups_controller_spec.rb
index d1279fe23fd..8a25aea5fd1 100644
--- a/spec/requests/groups_controller_spec.rb
+++ b/spec/requests/groups_controller_spec.rb
@@ -864,10 +864,20 @@ describe GroupsController do
         ))
       end
 
-      it "returns 404 if member is not found" do
-        put "/groups/#{group.id}/members.json", params: { usernames: 'some donkey' }
+      it "returns 400 if member is not found" do
+        [
+          { usernames: "some thing" },
+          { user_ids: "-5,-6" },
+          { user_emails: "some@test.org" }
+        ].each do |params|
+          put "/groups/#{group.id}/members.json", params: params
 
-        expect(response.status).to eq(404)
+          expect(response.status).to eq(400)
+
+          body = JSON.parse(response.body)
+
+          expect(body["error_type"]).to eq("invalid_parameters")
+        end
       end
 
       context 'public group' do