diff --git a/app/services/user_merger.rb b/app/services/user_merger.rb
index d745bc0e7cc..c8e8cc530ec 100644
--- a/app/services/user_merger.rb
+++ b/app/services/user_merger.rb
@@ -347,7 +347,11 @@ class UserMerger
 
   def delete_source_user
     @source_user.reload
-    @source_user.update_attribute(:admin, false)
+    @source_user.update_attributes(
+      admin: false,
+      email: "#{@source_user.username}_#{SecureRandom.hex}@no-email.invalid"
+    )
+
     UserDestroyer.new(Discourse.system_user).destroy(@source_user)
   end
 
diff --git a/spec/services/user_merger_spec.rb b/spec/services/user_merger_spec.rb
index 2d81ad8e3be..6306291138b 100644
--- a/spec/services/user_merger_spec.rb
+++ b/spec/services/user_merger_spec.rb
@@ -953,6 +953,15 @@ describe UserMerger do
     expect(User.find_by_username(source_user.username)).to be_nil
   end
 
+  it "deletes the source user even when it is a member of a group that grants a trust level" do
+    group = Fabricate(:group, grant_trust_level: 3)
+    group.bulk_add([source_user.id, target_user.id])
+
+    merge_users!
+
+    expect(User.find_by_username(source_user.username)).to be_nil
+  end
+
   it "deletes external auth infos of source user" do
     FacebookUserInfo.create(user_id: source_user.id, facebook_user_id: "example")
     GithubUserInfo.create(user_id: source_user.id, screen_name: "example", github_user_id: "examplel123123")