Migration multiple foreign keys

I'm just realised that even though I've set two foreign keys in my migration only the second one gets actually added.

Here's my schema:

Schema::create('favorites', function (Blueprint $table) {

    $table->integer('lecture_id')->unsigned();
    $table->integer('user_id')->unsigned();
    $table->timestamps();

    $table->primary(['lecture_id', 'user_id']);

    $table->foreign('lecture_id')
          ->references('id')->on('lectures')
          ->onDelete('cascade');

    $table->foreign('user_id')
          ->references('id')->on('users')
          ->onDelete('cascade');

});

I get both primary keys and only watched_user_id_foreign for the foreign constraint. Any idea why?