laravel error 150 foreign key constraint is incorrectly formed

I get the error:

SQLSTATE[HY000]: General error: 1005 Can't create table monkeybussiness.#sql-db0_17 (errno: 150 "Foreign key co nstraint is incorrectly formed")

while the columns are identical as far as I know. Why is this happening?

Events migrations file:

<?php

use Illuminate\Support\Facades\Schema;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Database\Migrations\Migration;

class CreateEventsTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('events', function (Blueprint $table) {
            $table->increments('afspraak_id');
            $table->timestamps();
            $table->string('titel');
            $table->integer('persoon_id');
            $table->foreign('persoon_id')->references('persoon_id')->on('personen');
        });
    }

    /**
     * Reverse the migrations.
     *
     * @return void
     */
    public function down()
    {
        Schema::dropIfExists('events');
    }
}

Personen migrations file:

<?php

use Illuminate\Support\Facades\Schema;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Database\Migrations\Migration;

class Personen extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('personen', function (Blueprint $table) {
            $table->increments('persoon_id');
            $table->timestamps();
            $table->string('voornaam');
            $table->string('achternaam');
            $table->string('email')->unique();
        });
    }

    /**
     * Reverse the migrations.
     *
     * @return void
     */
    public function down()
    {
        //
    }
}

I tried ->unsigned() but that doesn't work either.

via Sinan Samet