这里是我的两张表video和video_series但是在迁移时会报1215错误

error: 1215 Cannot add foreign key constraint

这是我的两张表
video迁移表

public function up()
    {
        Schema::create('videos', function (Blueprint $table) {
            $table->increments('id');
            $table->integer('video_series_id')->unsigned();
            $table->string('title');
            $table->string('intro');
            $table->string('poster');
            $table->string('url');
            $table->foreign('video_series_id')
                  ->references('id')
                  ->on('video_series')
                  ->onDelete('cascade')
                  ->onUpdate('cascade');
            $table->timestamps();
        });
    }

video_series迁移表

    public function up()
    {
        Schema::create('video_series', function (Blueprint $table) {
            $table->increments('id');
            $table->string('name');
            $table->string('thumbnail');
            $table->string('intro');
            $table->timestamps();
        });
    }