Android, Change overflow icon in custom ActionBar?

Question

I have a custom action bar, as follows:

<style name="ActionBar.Solid.pt" parent="@style/Widget.AppCompat.Light.ActionBar.Solid">
    <item name="background">@drawable/ab_solid_pt</item>
    <item name="backgroundStacked">@drawable/ab_stacked_solid_pt</item>
    <item name="backgroundSplit">@drawable/ab_bottom_solid_pt</item>
    <item name="progressBarStyle">@style/ProgressBar.pt</item>
    <item name="titleTextStyle">@style/ActionBar.Solid.pt.TitleTextStyle</item>
    <item name="android:actionOverflowButtonStyle">@style/OverFlow</item>
</style>

<style name="OverFlow" parent="@style/Widget.AppCompat.Light.ActionButton.Overflow">
    <item name="android:src">@drawable/customicon</item>
</style>

But the Overflow Icon is not changing from the default three dots. How can I set it to the custom image?

I'm modelling it after this SO post, but still not working out.

From Gradle:

compileSdkVersion 21
buildToolsVersion "21.1.2"

minSdkVersion 14
targetSdkVersion 21
versionCode 1
versionName "1.0"

compile 'com.android.support:appcompat-v7:21.0.3'

Thanks in advance.