diff --git a/astrid/plugin-src/com/todoroo/astrid/actfm/EditPeopleControlSet.java b/astrid/plugin-src/com/todoroo/astrid/actfm/EditPeopleControlSet.java
index eafe4c02a..e7404a7dd 100644
--- a/astrid/plugin-src/com/todoroo/astrid/actfm/EditPeopleControlSet.java
+++ b/astrid/plugin-src/com/todoroo/astrid/actfm/EditPeopleControlSet.java
@@ -707,6 +707,57 @@ public class EditPeopleControlSet extends PopupControlSet {
             if(!TextUtils.isEmpty(assignedCustom.getText())) {
                 userJson = PeopleContainer.createUserJson(assignedCustom);
                 assignedView = assignedCustom;
+                if (actFmPreferenceService.isLoggedIn()) {
+                    // check if the custom-user is already a member of this list
+                    TodorooCursor<Metadata> tags = TagService.getInstance().getTags(task.getId(), true);
+                        Metadata metadata = new Metadata();
+                        for(tags.moveToFirst(); !tags.isAfterLast(); tags.moveToNext()) {
+                            metadata.readFromCursor(tags);
+                            final String tag = metadata.getValue(TagService.TAG);
+                            final TagData tagData = tagDataService.getTag(tag, TagData.MEMBER_COUNT, TagData.MEMBERS, TagData.USER);
+                            if(tagData != null) {
+                                String customUserEmail = userJson.optString("email", "");
+                                final JSONArray membersFromTag = new JSONArray(tagData.getValue(TagData.MEMBERS));
+                                boolean customUserIsMember = false;
+                                for(int i = 0; i < membersFromTag.length(); i++) {
+                                    JSONObject member = membersFromTag.getJSONObject(i);
+                                    String email = member.optString("mail", "");
+                                    if (!TextUtils.isEmpty(email) && email.equals(customUserEmail)) {
+                                        customUserIsMember = true;
+                                        break;
+                                    }
+                                }
+
+                                if (!customUserIsMember) {
+                                    // show dialog to ask if user should be added to the tag-members
+                                    final JSONObject newMember = userJson;
+                                    DialogInterface.OnClickListener okListener = new DialogInterface.OnClickListener() {
+                                        @Override
+                                        public void onClick(DialogInterface d, int which) {
+                                            membersFromTag.put(newMember);
+                                            tagData.setValue(TagData.MEMBERS, membersFromTag.toString());
+                                            tagData.setValue(TagData.MEMBER_COUNT, membersFromTag.length());
+                                            tagDataService.save(tagData);
+                                        }
+                                    };
+
+                                    DialogInterface.OnClickListener cancelListener = new DialogInterface.OnClickListener() {
+                                        @Override
+                                        public void onClick(DialogInterface d, int which) {
+                                            // nothing to do here
+                                        }
+                                    };
+                                    DialogUtilities.okCancelCustomDialog(activity,
+                                            activity.getString(R.string.actfm_EPA_add_person_to_list_title),
+                                            activity.getString(R.string.actfm_EPA_add_person_to_list, customUserEmail, customUserEmail),
+                                            R.string.actfm_EPA_add_person_to_list_ok,
+                                            R.string.actfm_EPA_add_person_to_list_cancel,
+                                            android.R.drawable.ic_dialog_alert,
+                                            okListener, cancelListener);
+                                }
+                            }
+                        }
+                }
             } else {
                 if (!loadedUI || assignedList.getCheckedItemPosition() == ListView.INVALID_POSITION)
                     return true;
diff --git a/astrid/res/values-de/strings.xml b/astrid/res/values-de/strings.xml
index d0966d782..d69d01ce2 100644
--- a/astrid/res/values-de/strings.xml
+++ b/astrid/res/values-de/strings.xml
@@ -51,6 +51,10 @@
   <string name="actfm_EPA_login_to_share">Sie müssen auf Astrid.com angemeldet sein, um Aufgaben zu teilen.</string>
   <string name="actfm_EPA_login_button">Anmelden</string>
   <string name="actfm_EPA_dont_share_button">Nicht teilen.</string>
+  <string name="actfm_EPA_add_person_to_list_title">Aufgabe zugewiesen</string>
+  <string name="actfm_EPA_add_person_to_list">%1$s ist kein Mitglied dieser Liste. Möchten Sie %2$s zu dieser Liste hinzufügen?</string>
+  <string name="actfm_EPA_add_person_to_list_ok">Hinzufügen</string>
+  <string name="actfm_EPA_add_person_to_list_cancel">Nicht hinzufügen</string>
   <string name="actfm_ALA_title">Willkommen bei Astrid.com!</string>
   <string name="actfm_ALA_body">Astrid.com lässt Sie ihre Aufgaben online abrufen, teilen, und auf andere übertragen.</string>
   <string name="actfm_ALA_fb_login">Mit Facebook verbinden</string>
diff --git a/astrid/res/values/strings-actfm.xml b/astrid/res/values/strings-actfm.xml
index 7e2a5fe98..3310c5867 100644
--- a/astrid/res/values/strings-actfm.xml
+++ b/astrid/res/values/strings-actfm.xml
@@ -211,7 +211,14 @@
   
   <string name="actfm_EPA_dont_share_button">Don\'t share</string>
   
+  <string name="actfm_EPA_add_person_to_list_title">Task assigned</string>
+  
+  <string name="actfm_EPA_add_person_to_list">%1$s is not shared on this list. Would you like to add %2$s to this list?</string>
 
+  <string name="actfm_EPA_add_person_to_list_ok">Add to list</string>
+  
+  <string name="actfm_EPA_add_person_to_list_cancel">Don\'t add</string>
+  
   <!-- ========================================= sharing login activity == -->
 
   <!-- share login: Title -->