diff --git a/classes/Foreign_user.php b/classes/Foreign_user.php
index ec36dc3423..eeaf817876 100644
--- a/classes/Foreign_user.php
+++ b/classes/Foreign_user.php
@@ -70,33 +70,4 @@ class Foreign_user extends Managed_DataObject
             return empty($result) ? null : $fuser;
         }
     }
-
-    function updateKeys(&$orig)
-    {
-        $this->_connect();
-        $parts = array();
-        foreach (array('id', 'service', 'uri', 'nickname') as $k) {
-            if (strcmp($this->$k, $orig->$k) != 0) {
-                $parts[] = $k . ' = ' . $this->_quote($this->$k);
-            }
-        }
-        if (count($parts) == 0) {
-            // No changes
-            return true;
-        }
-        $toupdate = implode(', ', $parts);
-
-        $table = $this->tableName();
-        if(common_config('db','quote_identifiers')) {
-            $table = '"' . $table . '"';
-        }
-        $qry = 'UPDATE ' . $table . ' SET ' . $toupdate .
-          ' WHERE id = ' . $this->id;
-        $orig->decache();
-        $result = $this->query($qry);
-        if ($result) {
-            $this->encache();
-        }
-        return $result;
-    }
 }
diff --git a/classes/Managed_DataObject.php b/classes/Managed_DataObject.php
index 531232332d..d20d3cc27e 100644
--- a/classes/Managed_DataObject.php
+++ b/classes/Managed_DataObject.php
@@ -320,4 +320,35 @@ abstract class Managed_DataObject extends Memcached_DataObject
         // FIXME: How about forcing to return an int? Or will that overflow eventually?
         return $this->id;
     }
+
+    // 'update' won't write key columns, so we have to do it ourselves.
+    public function updateKeys(&$orig)
+    {
+        if (!$orig instanceof $this) {
+            throw new ServerException('Tried updating a DataObject with a different class than itself.');
+        }
+
+        $this->_connect();
+        $parts = array();
+        foreach ($this->keys() as $k) {
+            if (strcmp($this->$k, $orig->$k) != 0) {
+                $parts[] = $k . ' = ' . $this->_quote($this->$k);
+            }
+        }
+        if (count($parts) == 0) {
+            // No changes
+            return true;
+        }
+        $toupdate = implode(', ', $parts);
+
+        $table = common_database_tablename($this->tableName());
+        $qry = 'UPDATE ' . $table . ' SET ' . $toupdate .
+          ' WHERE id = ' . $this->getID();
+        $orig->decache();
+        $result = $this->query($qry);
+        if ($result !== false) {
+            $this->encache();
+        }
+        return $result;
+    }
 }
diff --git a/classes/User.php b/classes/User.php
index 242873efe1..060a67411d 100644
--- a/classes/User.php
+++ b/classes/User.php
@@ -152,34 +152,6 @@ class User extends Managed_DataObject
         return $this->getProfile()->hasPendingSubscription($other);
     }
 
-    // 'update' won't write key columns, so we have to do it ourselves.
-
-    function updateKeys(&$orig)
-    {
-        $this->_connect();
-        $parts = array();
-        foreach (array('nickname', 'email', 'incomingemail', 'sms', 'carrier', 'smsemail') as $k) {
-            if (strcmp($this->$k, $orig->$k) != 0) {
-                $parts[] = $k . ' = ' . $this->_quote($this->$k);
-            }
-        }
-        if (count($parts) == 0) {
-            // No changes
-            return true;
-        }
-        $toupdate = implode(', ', $parts);
-
-        $table = common_database_tablename($this->tableName());
-        $qry = 'UPDATE ' . $table . ' SET ' . $toupdate .
-          ' WHERE id = ' . $this->id;
-        $orig->decache();
-        $result = $this->query($qry);
-        if ($result) {
-            $this->encache();
-        }
-        return $result;
-    }
-
     /**
      * Get the most recent notice posted by this user, if any.
      *