diff --git a/priv/repo/migrations/20200804183107_add_unique_index_to_app_client_id.exs b/priv/repo/migrations/20200804183107_add_unique_index_to_app_client_id.exs
new file mode 100644
index 000000000..83de18096
--- /dev/null
+++ b/priv/repo/migrations/20200804183107_add_unique_index_to_app_client_id.exs
@@ -0,0 +1,7 @@
+defmodule Pleroma.Repo.Migrations.AddUniqueIndexToAppClientId do
+  use Ecto.Migration
+
+  def change do
+    create(unique_index(:apps, [:client_id]))
+  end
+end
diff --git a/test/web/oauth/app_test.exs b/test/web/oauth/app_test.exs
index 899af648e..993a490e0 100644
--- a/test/web/oauth/app_test.exs
+++ b/test/web/oauth/app_test.exs
@@ -29,5 +29,16 @@ test "gets exist app and updates scopes" do
       assert exist_app.id == app.id
       assert exist_app.scopes == ["read", "write", "follow", "push"]
     end
+
+    test "has unique client_id" do
+      insert(:oauth_app, client_name: "", redirect_uris: "", client_id: "boop")
+
+      error =
+        catch_error(insert(:oauth_app, client_name: "", redirect_uris: "", client_id: "boop"))
+
+      assert %Ecto.ConstraintError{} = error
+      assert error.constraint == "apps_client_id_index"
+      assert error.type == :unique
+    end
   end
 end