diff --git a/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/Constants.java b/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/Constants.java
index f681769b9..0df7a425b 100644
--- a/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/Constants.java
+++ b/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/Constants.java
@@ -142,6 +142,7 @@ public final class Constants {
         public static final String KEY_SIGNATURES_TABLE_INITIALIZED = "key_signatures_table_initialized";
 
         public static final class Theme {
+            public static final String AUTO = "auto";
             public static final String LIGHT = "light";
             public static final String DARK = "dark";
             public static final String DEFAULT = Constants.Pref.Theme.LIGHT;
diff --git a/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/ui/util/ThemeChanger.java b/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/ui/util/ThemeChanger.java
index 065896d71..efa26ba95 100644
--- a/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/ui/util/ThemeChanger.java
+++ b/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/ui/util/ThemeChanger.java
@@ -19,6 +19,7 @@ package org.sufficientlysecure.keychain.ui.util;
 
 import android.app.Activity;
 import android.content.Context;
+import android.content.res.Configuration;
 import android.view.ContextThemeWrapper;
 
 import org.sufficientlysecure.keychain.Constants;
@@ -33,13 +34,35 @@ public class ThemeChanger {
     private int mLightResId;
     private int mDarkResId;
 
+    static private boolean isDark(final Preferences preferences, final Configuration config) {
+        final String preferedTheme = preferences.getTheme();
+        switch (preferedTheme) {
+            case Constants.Pref.Theme.AUTO:
+                final int currentNightMode = config.uiMode & Configuration.UI_MODE_NIGHT_MASK;
+                switch (currentNightMode) {
+                    case Configuration.UI_MODE_NIGHT_NO:
+                        return false;
+                    case Configuration.UI_MODE_NIGHT_YES:
+                        return true;
+                    default:
+                        throw new IllegalStateException("Unknown uiMode");
+                }
+            case Constants.Pref.Theme.LIGHT:
+                return false;
+            case Constants.Pref.Theme.DARK:
+                return true;
+            default:
+                throw new IllegalStateException("Unknown theme");
+        }
+    }
+
     static public ContextThemeWrapper getDialogThemeWrapper(Context context) {
         Preferences preferences = Preferences.getPreferences(context);
 
         // if the dialog is displayed from the application class, design is missing.
         // hack to get holo design (which is not automatically applied due to activity's
         // Theme.NoDisplay)
-        if (Constants.Pref.Theme.DARK.equals(preferences.getTheme())) {
+        if (isDark(preferences, context.getResources().getConfiguration())) {
             return new ContextThemeWrapper(context, R.style.Theme_Keychain_Dark);
         } else {
             return new ContextThemeWrapper(context, R.style.Theme_Keychain_Light);
@@ -63,7 +86,11 @@ public class ThemeChanger {
      * the caller can re-create the activity, if need be.
      */
     public boolean changeTheme() {
-        String newTheme = mPreferences.getTheme();
+        String newTheme = Constants.Pref.Theme.LIGHT;
+        if (isDark(mPreferences, mContext.getResources().getConfiguration())) {
+            newTheme = Constants.Pref.Theme.DARK;
+        }
+
         if (mCurrentTheme != null && mCurrentTheme.equals(newTheme)) {
             return false;
         }
diff --git a/OpenKeychain/src/main/res/layout/main_activity.xml b/OpenKeychain/src/main/res/layout/main_activity.xml
index c620d999f..90b1b5242 100644
--- a/OpenKeychain/src/main/res/layout/main_activity.xml
+++ b/OpenKeychain/src/main/res/layout/main_activity.xml
@@ -14,7 +14,7 @@
         android:background="?attr/colorPrimary"
         android:minHeight="?attr/actionBarSize"
         android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
-        app:popupTheme="@style/ThemeOverlay.AppCompat.Light"
+        app:popupTheme="?popupOverlayStyle"
         tools:ignore="UnusedAttribute" />
 
     <FrameLayout
diff --git a/OpenKeychain/src/main/res/layout/view_key_activity.xml b/OpenKeychain/src/main/res/layout/view_key_activity.xml
index 889bfff78..ebb11f60c 100644
--- a/OpenKeychain/src/main/res/layout/view_key_activity.xml
+++ b/OpenKeychain/src/main/res/layout/view_key_activity.xml
@@ -150,7 +150,7 @@
                 android:touchscreenBlocksFocus="false"
                 android:transitionGroup="false"
                 app:layout_collapseMode="pin"
-                app:popupTheme="@style/ThemeOverlay.AppCompat.Light"
+                app:popupTheme="?popupOverlayStyle"
                 tools:ignore="UnusedAttribute" />
         </com.google.android.material.appbar.CollapsingToolbarLayout>
 
diff --git a/OpenKeychain/src/main/res/values/arrays.xml b/OpenKeychain/src/main/res/values/arrays.xml
index 584d773b7..bf43600e6 100644
--- a/OpenKeychain/src/main/res/values/arrays.xml
+++ b/OpenKeychain/src/main/res/values/arrays.xml
@@ -32,11 +32,15 @@
     </string-array>
 
     <string-array name="theme_entries" translatable="false">
-        <item>@string/theme_dark</item>
+        <item>@string/theme_auto</item>
         <item>@string/theme_light</item>
+        <item>@string/theme_dark</item>
     </string-array>
     <string-array name="theme_values" translatable="false">
+        <item>"auto"</item>
         <item>"dark"</item>
         <item>"light"</item>
     </string-array>
+
+    <attr name="popupOverlayStyle" format="reference" />
 </resources>
diff --git a/OpenKeychain/src/main/res/values/strings.xml b/OpenKeychain/src/main/res/values/strings.xml
index a4b50a495..a6b7ff9fd 100644
--- a/OpenKeychain/src/main/res/values/strings.xml
+++ b/OpenKeychain/src/main/res/values/strings.xml
@@ -314,8 +314,9 @@
     <string name="usage_sign_and_encrypt">"Sign &amp; Encrypt"</string>
     <string name="error">"Error"</string>
     <string name="error_message">"Error: %s"</string>
-    <string name="theme_dark">"Dark"</string>
+    <string name="theme_auto">"Automatic"</string>
     <string name="theme_light">"Light"</string>
+    <string name="theme_dark">"Dark"</string>
     <string name="strip">"Strip it"</string>
 
     <!-- sentences -->
diff --git a/OpenKeychain/src/main/res/values/themes.xml b/OpenKeychain/src/main/res/values/themes.xml
index f62238945..8bd07c50b 100644
--- a/OpenKeychain/src/main/res/values/themes.xml
+++ b/OpenKeychain/src/main/res/values/themes.xml
@@ -7,6 +7,8 @@
         <item name="colorAccent">#2196f3</item>
         <item name="colorBrightToolbar">#dddddd</item>
 
+        <item name="popupOverlayStyle">@style/ThemeOverlay.AppCompat.Light</item>
+
         <item name="colorFab">#2196f3</item>
         <item name="colorFabPressed">#1976d2</item>
         <item name="colorFabText">#fafafa</item>
@@ -48,6 +50,8 @@
         <item name="colorAccent">#2196f3</item>
         <item name="colorBrightToolbar">#808080</item>
 
+        <item name="popupOverlayStyle">@style/ThemeOverlay.AppCompat.Dark</item>
+
         <item name="colorFab">#2196f3</item>
         <item name="colorFabPressed">#1976d2</item>
         <item name="colorFabText">#fafafa</item>