diff --git a/app/src/main/java/com/todoroo/astrid/service/Upgrader.java b/app/src/main/java/com/todoroo/astrid/service/Upgrader.java
index 49ce35e4b..47608a8df 100644
--- a/app/src/main/java/com/todoroo/astrid/service/Upgrader.java
+++ b/app/src/main/java/com/todoroo/astrid/service/Upgrader.java
@@ -1,6 +1,10 @@
 package com.todoroo.astrid.service;
 
 import static com.google.common.base.Strings.isNullOrEmpty;
+import static com.google.common.collect.Iterables.transform;
+import static com.google.common.collect.Lists.newArrayList;
+import static com.google.common.collect.Sets.newHashSet;
+import static org.tasks.caldav.CaldavUtils.applyRelatedTo;
 import static org.tasks.db.DbUtils.batch;
 
 import android.os.Environment;
@@ -19,6 +23,7 @@ import org.tasks.analytics.Tracker;
 import org.tasks.analytics.Tracking;
 import org.tasks.caldav.CaldavUtils;
 import org.tasks.data.CaldavDao;
+import org.tasks.data.CaldavTask;
 import org.tasks.data.CaldavTaskContainer;
 import org.tasks.data.Filter;
 import org.tasks.data.FilterDao;
@@ -47,6 +52,7 @@ public class Upgrader {
   private static final int V6_7 = 585;
   private static final int V6_8_1 = 607;
   private static final int V6_9 = 608;
+  private static final int V6_10 = 617;
   private final Preferences preferences;
   private final Tracker tracker;
   private final TagDataDao tagDataDao;
@@ -96,6 +102,7 @@ public class Upgrader {
       run(from, V6_7, this::migrateGoogleTaskFilters);
       run(from, V6_8_1, this::migrateCaldavFilters);
       run(from, V6_9, this::applyCaldavCategories);
+      run(from, V6_10, this::applyCaldavSubtasks);
       tracker.reportEvent(Tracking.Events.UPGRADE, Integer.toString(from));
     }
     preferences.setCurrentVersion(to);
@@ -108,6 +115,27 @@ public class Upgrader {
     }
   }
 
+  private void applyCaldavSubtasks() {
+    List<CaldavTask> updated = newArrayList();
+
+    for (CaldavTask task : transform(caldavDao.getTasks(), CaldavTaskContainer::getCaldavTask)) {
+      at.bitfire.ical4android.Task remoteTask = CaldavUtils.fromVtodo(task.getVtodo());
+      if (remoteTask == null) {
+        continue;
+      }
+      applyRelatedTo(task, remoteTask);
+      if (!Strings.isNullOrEmpty(task.getRemoteParent())) {
+        updated.add(task);
+      }
+    }
+
+    caldavDao.update(updated);
+
+    for (String calendar : newHashSet(transform(updated, CaldavTask::getCalendar))) {
+      caldavDao.updateParents(calendar);
+    }
+  }
+
   private void applyCaldavCategories() {
     List<Long> tasksWithTags = caldavDao.getTasksWithTags();
     for (CaldavTaskContainer container : caldavDao.getTasks()) {
diff --git a/app/src/main/java/org/tasks/caldav/CaldavSynchronizer.java b/app/src/main/java/org/tasks/caldav/CaldavSynchronizer.java
index 0f35320a9..120764644 100644
--- a/app/src/main/java/org/tasks/caldav/CaldavSynchronizer.java
+++ b/app/src/main/java/org/tasks/caldav/CaldavSynchronizer.java
@@ -7,6 +7,7 @@ import static com.google.common.collect.Lists.newArrayList;
 import static com.google.common.collect.Lists.transform;
 import static com.google.common.collect.Sets.difference;
 import static com.google.common.collect.Sets.newHashSet;
+import static org.tasks.caldav.CaldavUtils.applyRelatedTo;
 import static org.tasks.time.DateTimeUtils.currentTimeMillis;
 
 import android.content.Context;
@@ -42,7 +43,6 @@ import java.util.List;
 import java.util.Set;
 import javax.inject.Inject;
 import javax.net.ssl.SSLException;
-import net.fortuna.ical4j.model.Property;
 import net.fortuna.ical4j.model.property.ProdId;
 import okhttp3.HttpUrl;
 import okhttp3.OkHttpClient;
@@ -60,7 +60,6 @@ import org.tasks.data.TagDao;
 import org.tasks.data.TagData;
 import org.tasks.data.TagDataDao;
 import org.tasks.injection.ForApplication;
-import retrofit2.http.HEAD;
 import timber.log.Timber;
 
 public class CaldavSynchronizer {
@@ -377,13 +376,7 @@ public class CaldavSynchronizer {
     caldavTask.setEtag(eTag);
     caldavTask.setLastSync(DateUtilities.now() + 1000L);
 
-    // Process remote parents
-    LinkedList<Property> unknownProperties = remote.getUnknownProperties();
-    for (Property prop : unknownProperties) {
-      if (prop.getName().equals(Property.RELATED_TO)) {
-        caldavTask.setRemoteParent(prop.getValue());
-      }
-    }
+    applyRelatedTo(caldavTask, remote);
 
     if (caldavTask.getId() == Task.NO_ID) {
       caldavTask.setId(caldavDao.insert(caldavTask));
@@ -393,5 +386,4 @@ public class CaldavSynchronizer {
       Timber.d("UPDATE %s", caldavTask);
     }
   }
-
 }
diff --git a/app/src/main/java/org/tasks/caldav/CaldavUtils.java b/app/src/main/java/org/tasks/caldav/CaldavUtils.java
index 920401e43..1e8fdc979 100644
--- a/app/src/main/java/org/tasks/caldav/CaldavUtils.java
+++ b/app/src/main/java/org/tasks/caldav/CaldavUtils.java
@@ -9,6 +9,8 @@ import java.io.StringReader;
 import java.util.Collections;
 import java.util.List;
 import java.util.Set;
+import net.fortuna.ical4j.model.Property;
+import org.tasks.data.CaldavTask;
 import org.tasks.data.TagData;
 import org.tasks.data.TagDataDao;
 
@@ -33,4 +35,12 @@ public class CaldavUtils {
     }
     return selectedTags;
   }
+
+  public static void applyRelatedTo(CaldavTask caldavTask, at.bitfire.ical4android.Task remote) {
+    for (Property prop : remote.getUnknownProperties()) {
+      if (prop.getName().equals(Property.RELATED_TO)) {
+        caldavTask.setRemoteParent(prop.getValue());
+      }
+    }
+  }
 }
diff --git a/app/src/main/java/org/tasks/data/CaldavDao.java b/app/src/main/java/org/tasks/data/CaldavDao.java
index 6207ce6e2..d4ef98ff3 100644
--- a/app/src/main/java/org/tasks/data/CaldavDao.java
+++ b/app/src/main/java/org/tasks/data/CaldavDao.java
@@ -52,6 +52,9 @@ public abstract class CaldavDao {
   @Update
   public abstract void update(CaldavTask caldavTask);
 
+  @Update
+  public abstract void update(Iterable<CaldavTask> tasks);
+
   @Delete
   public abstract void delete(CaldavTask caldavTask);
 
diff --git a/app/src/main/java/org/tasks/data/CaldavTaskContainer.java b/app/src/main/java/org/tasks/data/CaldavTaskContainer.java
index eb6d8be79..344d81d0a 100644
--- a/app/src/main/java/org/tasks/data/CaldavTaskContainer.java
+++ b/app/src/main/java/org/tasks/data/CaldavTaskContainer.java
@@ -6,4 +6,8 @@ import com.todoroo.astrid.data.Task;
 public class CaldavTaskContainer {
   @Embedded public Task task;
   @Embedded public CaldavTask caldavTask;
+
+  public CaldavTask getCaldavTask() {
+    return caldavTask;
+  }
 }