diff --git a/app/src/main/java/com/etesync/syncadapter/App.java b/app/src/main/java/com/etesync/syncadapter/App.java
index b03c8d62..3c23658f 100644
--- a/app/src/main/java/com/etesync/syncadapter/App.java
+++ b/app/src/main/java/com/etesync/syncadapter/App.java
@@ -45,6 +45,8 @@ import com.etesync.syncadapter.model.Settings;
 import com.etesync.syncadapter.resource.LocalAddressBook;
 import com.etesync.syncadapter.resource.LocalCalendar;
 
+import net.fortuna.ical4j.util.UidGenerator;
+
 import org.apache.commons.lang3.time.DateFormatUtils;
 
 import java.io.File;
@@ -70,6 +72,7 @@ import lombok.Cleanup;
 import lombok.Getter;
 import okhttp3.internal.tls.OkHostnameVerifier;
 
+
 public class App extends Application {
     public static final String FLAVOR_GOOGLE_PLAY = "gplay";
 
@@ -92,18 +95,24 @@ public class App extends Application {
     @Getter
     private static HostnameVerifier hostnameVerifier;
 
+    @Getter
+    private static UidGenerator uidGenerator;
+
     public final static Logger log = Logger.getLogger("syncadapter");
     static {
         at.bitfire.cert4android.Constants.log = Logger.getLogger("syncadapter.cert4android");
     }
 
     @Override
+    @SuppressLint("HardwareIds")
     public void onCreate() {
         super.onCreate();
         reinitCertManager();
         reinitLogger();
         StrictMode.enableDefaults();
         initPrefVersion();
+
+        uidGenerator = new UidGenerator(null, android.provider.Settings.Secure.getString(getContentResolver(), android.provider.Settings.Secure.ANDROID_ID));
     }
 
     public void reinitCertManager() {
diff --git a/app/src/main/java/com/etesync/syncadapter/resource/LocalContact.java b/app/src/main/java/com/etesync/syncadapter/resource/LocalContact.java
index 044c1c2f..cece3018 100644
--- a/app/src/main/java/com/etesync/syncadapter/resource/LocalContact.java
+++ b/app/src/main/java/com/etesync/syncadapter/resource/LocalContact.java
@@ -28,6 +28,7 @@ import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.util.HashSet;
 import java.util.Set;
+import java.util.UUID;
 import java.util.logging.Level;
 
 import at.bitfire.vcard4android.AndroidAddressBook;
@@ -101,9 +102,10 @@ public class LocalContact extends AndroidContact implements LocalResource {
         }
     }
 
-    public void updateFileNameAndUID(String uid) throws ContactsStorageException {
+    public void prepareForUpload() throws ContactsStorageException {
         try {
-            String newFileName = uid;
+            final String uid = UUID.randomUUID().toString();
+            final String newFileName = uid;
 
             ContentValues values = new ContentValues(2);
             values.put(COLUMN_FILENAME, newFileName);
diff --git a/app/src/main/java/com/etesync/syncadapter/resource/LocalEvent.java b/app/src/main/java/com/etesync/syncadapter/resource/LocalEvent.java
index 6b92546c..8c95dfbb 100644
--- a/app/src/main/java/com/etesync/syncadapter/resource/LocalEvent.java
+++ b/app/src/main/java/com/etesync/syncadapter/resource/LocalEvent.java
@@ -11,6 +11,7 @@ package com.etesync.syncadapter.resource;
 import android.annotation.TargetApi;
 import android.content.ContentProviderOperation;
 import android.content.ContentValues;
+import android.database.Cursor;
 import android.net.Uri;
 import android.os.Build;
 import android.os.RemoteException;
@@ -31,6 +32,7 @@ import at.bitfire.ical4android.AndroidEventFactory;
 import at.bitfire.ical4android.CalendarStorageException;
 import at.bitfire.ical4android.Event;
 import at.bitfire.vcard4android.ContactsStorageException;
+import lombok.Cleanup;
 import lombok.Getter;
 import lombok.Setter;
 
@@ -134,9 +136,16 @@ public class LocalEvent extends AndroidEvent implements LocalResource {
 
     /* custom queries */
 
-    public void updateFileNameAndUID(String uid) throws CalendarStorageException {
+    public void prepareForUpload() throws CalendarStorageException {
         try {
-            String newFileName = uid;
+            String uid = null;
+            @Cleanup Cursor c = calendar.provider.query(eventSyncURI(), new String[] { Events.UID_2445 }, null, null, null);
+            if (c.moveToNext())
+                uid = c.getString(0);
+            if (uid == null)
+                uid = App.getUidGenerator().generateUid().getValue();
+
+            final String newFileName = uid;
 
             ContentValues values = new ContentValues(2);
             values.put(Events._SYNC_ID, newFileName);
diff --git a/app/src/main/java/com/etesync/syncadapter/resource/LocalGroup.java b/app/src/main/java/com/etesync/syncadapter/resource/LocalGroup.java
index bf104516..2f78570b 100644
--- a/app/src/main/java/com/etesync/syncadapter/resource/LocalGroup.java
+++ b/app/src/main/java/com/etesync/syncadapter/resource/LocalGroup.java
@@ -26,6 +26,7 @@ import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.util.LinkedList;
 import java.util.List;
+import java.util.UUID;
 import java.util.logging.Level;
 
 import com.etesync.syncadapter.App;
@@ -100,8 +101,9 @@ public class LocalGroup extends AndroidGroup implements LocalResource {
     }
 
     @Override
-    public void updateFileNameAndUID(String uid) throws ContactsStorageException {
-        String newFileName = uid + ".vcf";
+    public void prepareForUpload() throws ContactsStorageException {
+        final String uid = UUID.randomUUID().toString();
+        final String newFileName = uid + ".vcf";
 
         ContentValues values = new ContentValues(2);
         values.put(COLUMN_FILENAME, newFileName);
diff --git a/app/src/main/java/com/etesync/syncadapter/resource/LocalResource.java b/app/src/main/java/com/etesync/syncadapter/resource/LocalResource.java
index cf033d67..8bc8f284 100644
--- a/app/src/main/java/com/etesync/syncadapter/resource/LocalResource.java
+++ b/app/src/main/java/com/etesync/syncadapter/resource/LocalResource.java
@@ -25,7 +25,7 @@ public interface LocalResource {
 
     int delete() throws CalendarStorageException, ContactsStorageException;
 
-    void updateFileNameAndUID(String uuid) throws CalendarStorageException, ContactsStorageException;
+    void prepareForUpload() throws CalendarStorageException, ContactsStorageException;
     void clearDirty(String eTag) throws CalendarStorageException, ContactsStorageException;
 
 }
diff --git a/app/src/main/java/com/etesync/syncadapter/resource/LocalTask.java b/app/src/main/java/com/etesync/syncadapter/resource/LocalTask.java
index 0c28d9da..d7652ddd 100644
--- a/app/src/main/java/com/etesync/syncadapter/resource/LocalTask.java
+++ b/app/src/main/java/com/etesync/syncadapter/resource/LocalTask.java
@@ -14,6 +14,8 @@ import android.os.RemoteException;
 import android.provider.CalendarContract.Events;
 import android.support.annotation.NonNull;
 
+import com.etesync.syncadapter.App;
+
 import org.dmfs.provider.tasks.TaskContract.Tasks;
 
 import java.io.FileNotFoundException;
@@ -89,9 +91,10 @@ public class LocalTask extends AndroidTask implements LocalResource {
 
     /* custom queries */
 
-    public void updateFileNameAndUID(String uid) throws CalendarStorageException {
+    public void prepareForUpload() throws CalendarStorageException {
         try {
-            String newFileName = uid + ".ics";
+            final String uid = App.getUidGenerator().generateUid().getValue();
+            final String newFileName = uid + ".ics";
 
             ContentValues values = new ContentValues(2);
             values.put(Tasks._SYNC_ID, newFileName);
diff --git a/app/src/main/java/com/etesync/syncadapter/syncadapter/SyncManager.java b/app/src/main/java/com/etesync/syncadapter/syncadapter/SyncManager.java
index 6874df8b..7aeee7f8 100644
--- a/app/src/main/java/com/etesync/syncadapter/syncadapter/SyncManager.java
+++ b/app/src/main/java/com/etesync/syncadapter/syncadapter/SyncManager.java
@@ -40,7 +40,6 @@ import java.util.ArrayList;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.Locale;
-import java.util.UUID;
 import java.util.logging.Level;
 
 import at.bitfire.ical4android.CalendarStorageException;
@@ -428,9 +427,9 @@ abstract public class SyncManager {
             if (local.getUuid() != null) {
                 continue;
             }
-            String uuid = UUID.randomUUID().toString();
-            App.log.fine("Found local record #" + local.getId() + " without file name; assigning file name/UID based on " + uuid);
-            local.updateFileNameAndUID(uuid);
+
+            App.log.fine("Found local record #" + local.getId() + " without file name; generating file name/UID if necessary");
+            local.prepareForUpload();
         }
     }