diff --git a/packages/SystemUI/res/drawable-nodpi/compat_mode_help_bg.png b/packages/SystemUI/res/drawable-nodpi/compat_mode_help_bg.png
new file mode 100644
index 0000000000000..d1d32a470f0b0
Binary files /dev/null and b/packages/SystemUI/res/drawable-nodpi/compat_mode_help_bg.png differ
diff --git a/packages/SystemUI/res/drawable/compat_mode_help_diagram.png b/packages/SystemUI/res/drawable/compat_mode_help_diagram.png
new file mode 100644
index 0000000000000..e2122313bc55e
Binary files /dev/null and b/packages/SystemUI/res/drawable/compat_mode_help_diagram.png differ
diff --git a/packages/SystemUI/res/drawable/compat_mode_help_icon.png b/packages/SystemUI/res/drawable/compat_mode_help_icon.png
new file mode 100644
index 0000000000000..03bbef9c06a28
Binary files /dev/null and b/packages/SystemUI/res/drawable/compat_mode_help_icon.png differ
diff --git a/packages/SystemUI/res/layout-sw600dp/compat_mode_help.xml b/packages/SystemUI/res/layout-sw600dp/compat_mode_help.xml
new file mode 100644
index 0000000000000..df3c5a3a402d6
--- /dev/null
+++ b/packages/SystemUI/res/layout-sw600dp/compat_mode_help.xml
@@ -0,0 +1,79 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+/*
+** Copyright 2011, The Android Open Source Project
+**
+** Licensed under the Apache License, Version 2.0 (the "License"); 
+** you may not use this file except in compliance with the License. 
+** You may obtain a copy of the License at 
+**
+**     http://www.apache.org/licenses/LICENSE-2.0 
+**
+** Unless required by applicable law or agreed to in writing, software 
+** distributed under the License is distributed on an "AS IS" BASIS, 
+** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 
+** See the License for the specific language governing permissions and 
+** limitations under the License.
+*/
+-->
+
+<RelativeLayout
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    android:layout_height="match_parent"
+    android:layout_width="match_parent"
+    android:background="@drawable/compat_mode_help_bg"
+    >
+    <TextView
+        android:id="@+id/header"
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:layout_marginLeft="160dp"
+        android:layout_marginTop="80dp"
+        android:textSize="60sp"
+        android:maxLines="1"
+        android:shadowRadius="8"
+        android:shadowColor="#FF000000"
+        android:text="@string/compat_mode_help_header"
+        />
+    <ImageView
+        android:id="@+id/diagram"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_marginLeft="160dp"
+        android:layout_marginTop="80dp"
+        android:layout_centerInParent="true"
+        android:src="@drawable/compat_mode_help_diagram"
+        />
+    <TextView
+        android:id="@+id/explanation"
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:layout_marginBottom="80dp"
+        android:layout_marginRight="240dp"
+        android:layout_alignLeft="@id/header"
+        android:layout_alignParentBottom="true"
+        android:shadowRadius="4"
+        android:shadowColor="#FF000000"
+        android:textSize="28sp"
+        android:text="@string/compat_mode_help_body"
+        />
+    <ImageView
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_marginRight="80dp"
+        android:layout_alignBottom="@id/explanation"
+        android:layout_alignParentRight="true"
+        android:src="@drawable/compat_mode_help_icon"
+        />
+    <Button
+        android:id="@+id/button"
+        android:layout_width="208dp"
+        android:layout_height="48dp"
+        android:layout_alignLeft="@id/header"
+        android:layout_alignParentBottom="true"
+        android:layout_marginBottom="10dp"
+        android:textSize="28sp"
+        android:text="@android:string/ok"
+        />
+</RelativeLayout>
+
diff --git a/packages/SystemUI/res/values/strings.xml b/packages/SystemUI/res/values/strings.xml
index 973a4b2849ed5..8945da5828d94 100644
--- a/packages/SystemUI/res/values/strings.xml
+++ b/packages/SystemUI/res/values/strings.xml
@@ -150,4 +150,10 @@
     <!-- Checkbox label for application compatibility mode OFF (normal mode on tablets).
          [CHAR LIMIT=25] -->
     <string name="compat_mode_off">Stretch to fill screen</string>
+    
+    <!-- Compatibility mode help screen: header text. [CHAR LIMIT=50] -->
+    <string name="compat_mode_help_header">Compatibility Zoom</string>
+
+    <!-- Compatibility mode help screen: body text. [CHAR LIMIT=150] -->
+    <string name="compat_mode_help_body">When an app was designed for a smaller screen, a zoom control will appear by the clock.</string>
 </resources>
diff --git a/packages/SystemUI/src/com/android/systemui/statusbar/policy/Prefs.java b/packages/SystemUI/src/com/android/systemui/statusbar/policy/Prefs.java
index 05eafe866955c..83e8c96f8064b 100644
--- a/packages/SystemUI/src/com/android/systemui/statusbar/policy/Prefs.java
+++ b/packages/SystemUI/src/com/android/systemui/statusbar/policy/Prefs.java
@@ -26,6 +26,8 @@ public class Prefs {
     public static final String DO_NOT_DISTURB_PREF = "do_not_disturb";
     public static final boolean DO_NOT_DISTURB_DEFAULT = false;
 
+    public static final String SHOWN_COMPAT_MODE_HELP = "shown_compat_mode_help";
+
     public static SharedPreferences read(Context context) {
         return context.getSharedPreferences(Prefs.SHARED_PREFS_NAME, Context.MODE_PRIVATE);
     }
diff --git a/packages/SystemUI/src/com/android/systemui/statusbar/tablet/TabletStatusBar.java b/packages/SystemUI/src/com/android/systemui/statusbar/tablet/TabletStatusBar.java
index 412cfc7944c12..eef440c59c9c3 100644
--- a/packages/SystemUI/src/com/android/systemui/statusbar/tablet/TabletStatusBar.java
+++ b/packages/SystemUI/src/com/android/systemui/statusbar/tablet/TabletStatusBar.java
@@ -23,6 +23,7 @@ import java.util.ArrayList;
 import android.animation.LayoutTransition;
 import android.animation.ObjectAnimator;
 import android.app.ActivityManagerNative;
+import android.app.Dialog;
 import android.app.PendingIntent;
 import android.app.Notification;
 import android.app.StatusBarManager;
@@ -35,6 +36,7 @@ import android.inputmethodservice.InputMethodService;
 import android.graphics.PixelFormat;
 import android.graphics.Rect;
 import android.graphics.drawable.LayerDrawable;
+import android.provider.Settings;
 import android.os.Handler;
 import android.os.IBinder;
 import android.os.Message;
@@ -1005,8 +1007,43 @@ public class TabletStatusBar extends StatusBar implements
         // See above re: lights-out policy for legacy apps.
         if (windowVisible) setLightsOn(true);
 
-        // XXX: this is broken: http://b/4603422
         mCompatModeButton.refresh();
+        if (mCompatModeButton.getVisibility() == View.VISIBLE) {
+            if (! Prefs.read(mContext).getBoolean(Prefs.SHOWN_COMPAT_MODE_HELP, false)) {
+                showCompatibilityHelp();
+            }
+        }
+    }
+
+    private void showCompatibilityHelp() {
+        final View dlg = View.inflate(mContext, R.layout.compat_mode_help, null);
+        View button = dlg.findViewById(R.id.button);
+
+        button.setOnClickListener(new View.OnClickListener() {
+            @Override
+            public void onClick(View v) {
+                WindowManagerImpl.getDefault().removeView(dlg);
+            }
+        });
+
+        WindowManager.LayoutParams lp = mNotificationPanelParams = new WindowManager.LayoutParams(
+                ViewGroup.LayoutParams.MATCH_PARENT,
+                ViewGroup.LayoutParams.MATCH_PARENT,
+                WindowManager.LayoutParams.TYPE_SYSTEM_DIALOG,
+                WindowManager.LayoutParams.FLAG_LAYOUT_IN_SCREEN
+                    | WindowManager.LayoutParams.FLAG_LAYOUT_NO_LIMITS
+                    | WindowManager.LayoutParams.FLAG_ALT_FOCUSABLE_IM,
+                PixelFormat.TRANSLUCENT);
+        lp.setTitle("CompatibilityModeDialog");
+        lp.softInputMode = WindowManager.LayoutParams.SOFT_INPUT_STATE_UNCHANGED
+                | WindowManager.LayoutParams.SOFT_INPUT_ADJUST_NOTHING;
+        lp.windowAnimations = com.android.internal.R.style.Animation_ZoomButtons; // simple fade
+
+        WindowManagerImpl.getDefault().addView(dlg, lp);
+
+        SharedPreferences.Editor editor = Prefs.edit(mContext);
+        editor.putBoolean(Prefs.SHOWN_COMPAT_MODE_HELP, true);
+        editor.apply();
     }
 
     public void setImeWindowStatus(IBinder token, int vis, int backDisposition) {