diff --git a/lib/Doctrine/ORM/Internal/Hydration/ObjectHydrator.php b/lib/Doctrine/ORM/Internal/Hydration/ObjectHydrator.php
index 019d1a2463..8772449fce 100644
--- a/lib/Doctrine/ORM/Internal/Hydration/ObjectHydrator.php
+++ b/lib/Doctrine/ORM/Internal/Hydration/ObjectHydrator.php
@@ -394,8 +394,10 @@ protected function hydrateRowData(array $row, array &$result)
                                     $reflFieldValue->hydrateSet($indexValue, $element);
                                     $this->identifierMap[$path][$id[$parentAlias]][$id[$dqlAlias]] = $indexValue;
                                 } else {
-                                    $reflFieldValue->hydrateAdd($element);
-                                    $reflFieldValue->last();
+                                    if (! $reflFieldValue->contains($element)) {
+                                        $reflFieldValue->hydrateAdd($element);
+                                        $reflFieldValue->last();
+                                    }
                                     $this->identifierMap[$path][$id[$parentAlias]][$id[$dqlAlias]] = $reflFieldValue->key();
                                 }