Android - Spinner arrow does not show when background is imageview

I have a simple layout where I'm using Imageview as background because I want to use the property "scaleType". I Placed the Imageview first in my relative layout and placed the Spinner right after.

The spinner arrow does not show. If I'm removing the the Imageview or placing my image as a background image (in the relative layout) it will show.

Here is my layout:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@color/White">

<RelativeLayout
    android:layout_width="match_parent"
    android:layout_height="400dp"
    android:layout_centerHorizontal="true"
    android:layout_centerVertical="true"
    android:layout_marginLeft="7dp"
    android:layout_marginRight="7dp">

    <ImageView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:scaleType="matrix"
        android:src="@drawable/background" />

    <Spinner
        android:id="@+id/spinnerGameType"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentRight="true"
        android:spinnerMode="dropdown"
        android:theme="@style/ThemeOverlay.AppCompat.Light" />

</RelativeLayout>