diff --git a/classes/Notice.php b/classes/Notice.php
index fd3a98f1f7..0074a37bdf 100644
--- a/classes/Notice.php
+++ b/classes/Notice.php
@@ -417,8 +417,9 @@ class Notice extends Managed_DataObject
     static function saveNew($profile_id, $content, $source, array $options=null) {
         $defaults = array('uri' => null,
                           'url' => null,
-                          'reply_to' => null,
-                          'repeat_of' => null,
+                          'conversation' => null,   // URI of conversation
+                          'reply_to' => null,       // This will override convo URI if the parent is known
+                          'repeat_of' => null,      // This will override convo URI if the repeated notice is known
                           'scope' => null,
                           'distribute' => true,
                           'object_type' => null,
@@ -600,6 +601,17 @@ class Notice extends Managed_DataObject
 
                 // Scope set below
             }
+
+            // If we don't know the reply, we might know the conversation!
+            // This will happen if a known remote user replies to an
+            // unknown remote user - within a known conversation.
+            if (empty($notice->conversation) and !empty($options['conversation'])) {
+                $conv = Conversation::getKV('uri', $options['conversation']);
+                if ($conv instanceof Conversation and $activity->time > $conv->created) {
+                    common_debug('Conversation stitched together from (probably) reply to unknown remote user. Activity creation time ('.$activity->time.') is greater than conversation creation time ('.$conv->created.').');
+                    $notice->conversation = $conv->id;
+                }
+            }
         }
 
         if (!empty($lat) && !empty($lon)) {
diff --git a/plugins/OStatus/classes/Ostatus_profile.php b/plugins/OStatus/classes/Ostatus_profile.php
index 7ddf1f4d8a..f7d4513a87 100644
--- a/plugins/OStatus/classes/Ostatus_profile.php
+++ b/plugins/OStatus/classes/Ostatus_profile.php
@@ -684,6 +684,10 @@ class Ostatus_profile extends Managed_DataObject
                     $options['reply_to'] = $orig->id;
                 }
             }
+            if (!empty($activity->context->conversation)) {
+                // we store the URI here, Notice class can look it up later
+                $options['conversation'] = $activity->context->conversation;
+            }
 
             $location = $activity->context->location;
             if ($location) {