How to fix FAB to the bottom of the dialog box?

I want to fix FAB at the bottom of the window. Ie, that one half was in the window, and the other on the blackout. Now the window layout looks like this

 <android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto" android:layout_width="fill_parent" android:layout_height="fill_parent" android:orientation="vertical"> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="fill_parent" android:layout_height="fill_parent" android:orientation="vertical" android:gravity="center" android:weightSum="100" android:id="@+id/alert_root" android:layout_marginBottom="10dp"> <LinearLayout android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_marginBottom="10dp"> <widget.CircleImageView android:layout_height="match_parent" android:layout_width="wrap_content" android:id="@+id/alert_photo" android:src="@drawable/image_1" android:background="@drawable/circle" android:layout_weight="75" android:layout_marginLeft="10dp"/> <LinearLayout android:layout_width="match_parent" android:layout_height="wrap_content" android:orientation="vertical" android:layout_marginLeft="10dp" android:gravity="right|center_vertical" android:layout_weight="25" android:layout_marginRight="10dp"> <android.support.design.widget.TextInputLayout android:id="@+id/alert_name" android:layout_width="match_parent" android:layout_height="wrap_content" android:textColorHint="#000000"> <android.support.v7.widget.AppCompatEditText android:id="@+id/input_name" android:layout_width="match_parent" android:layout_height="wrap_content" android:hint="Имя" android:textColor="#000000"/> </android.support.design.widget.TextInputLayout> <android.support.design.widget.TextInputLayout android:id="@+id/alert_family" android:layout_width="match_parent" android:textColorHint="#000000" android:layout_marginTop="7dp" android:layout_height="wrap_content"> <android.support.design.widget.TextInputEditText android:id="@+id/input_family" android:layout_width="match_parent" android:layout_height="wrap_content" android:hint="Фамилия" android:textColor="#000000"/> </android.support.design.widget.TextInputLayout> </LinearLayout> </LinearLayout> <android.support.design.widget.TextInputLayout android:id="@+id/alert_verbose" android:layout_width="match_parent" android:textColorHint="#000000" android:layout_marginTop="7dp" android:layout_height="wrap_content" android:layout_margin="10dp"> <android.support.design.widget.TextInputEditText android:id="@+id/input_verbose" android:layout_width="match_parent" android:layout_height="wrap_content" android:hint="Описание" android:textColor="#000000"/> </android.support.design.widget.TextInputLayout> </LinearLayout> <android.support.design.widget.FloatingActionButton android:layout_height="wrap_content" android:layout_width="wrap_content" android:id="@+id/done" app:backgroundTint="#F28A14" app:layout_anchor="@id/alert_root" android:src="@drawable/fab_add" app:layout_anchorGravity="top|end"/> </android.support.design.widget.CoordinatorLayout> 

Screenshot:

It seems to use the anchor correctly. But something is wrong ...