diff --git a/lib/Doctrine/ORM/ORMInvalidArgumentException.php b/lib/Doctrine/ORM/ORMInvalidArgumentException.php
index cb50376797a..249b6b2469a 100644
--- a/lib/Doctrine/ORM/ORMInvalidArgumentException.php
+++ b/lib/Doctrine/ORM/ORMInvalidArgumentException.php
@@ -187,6 +187,28 @@ public static function invalidIdentifierBindingEntity()
         return new self("Binding entities to query parameters only allowed for entities that have an identifier.");
     }
 
+    /**
+     * @param object $relation
+     * @param string $fieldname
+     * @param mixed $value
+     * @return self
+     */
+    public static function computeAssociationChangesError($relation, $fieldname, $value)
+    {
+        return new self(sprintf('Expected an Object for relation %s::%s got %s instead.', get_class($relation), $fieldname, gettype($value)));
+    }
+
+    /**
+     * @param \Doctrine\ORM\Mapping\ClassMetadata $targetClass
+     * @param array $assoc
+     * @param mixed $entry
+     * @return self
+     */
+    public static function invalidAssociation($targetClass, $assoc, $entry)
+    {
+        return new self(gettype($entry) . (is_scalar($entry) ? ' "'.$entry.'"': '') . ' is not an Object.');
+    }
+
     /**
      * Helper method to show an object as string.
      *
diff --git a/lib/Doctrine/ORM/UnitOfWork.php b/lib/Doctrine/ORM/UnitOfWork.php
index fd21c99ca2e..6df7f3d5aac 100644
--- a/lib/Doctrine/ORM/UnitOfWork.php
+++ b/lib/Doctrine/ORM/UnitOfWork.php
@@ -707,7 +707,11 @@ public function computeChangeSet(ClassMetadata $class, $entity)
                 continue;
             }
 
-            $this->computeAssociationChanges($assoc, $val);
+            try {
+                $this->computeAssociationChanges($assoc, $val);
+            } catch (\Exception $ex) {
+                throw ORMInvalidArgumentException::computeAssociationChangesError($entity, $assoc['fieldName'], $ex->value);
+            }
 
             if ( ! isset($this->entityChangeSets[$oid]) &&
                 $assoc['isOwningSide'] &&
@@ -809,6 +813,10 @@ private function computeAssociationChanges($assoc, $value)
         $targetClass    = $this->em->getClassMetadata($assoc['targetEntity']);
 
         foreach ($unwrappedValue as $key => $entry) {
+            if (! ($entry instanceof $targetClass->name)) {
+                throw ORMInvalidArgumentException::invalidAssociation($targetClass, $assoc, $entry);
+            }
+
             $state = $this->getEntityState($entry, self::STATE_NEW);
 
             if ( ! ($entry instanceof $assoc['targetEntity'])) {