diff --git a/core/dbobject.class.php b/core/dbobject.class.php
index fdf8ddba3..d4f2535cb 100644
--- a/core/dbobject.class.php
+++ b/core/dbobject.class.php
@@ -2297,15 +2297,19 @@ abstract class DBObject implements iDisplay
 				continue;
 			}
 
-			/** @noinspection NotOptimalIfConditionsInspection */
-			/** @noinspection TypeUnsafeComparisonInspection */
 			if (utils::IsNullOrEmptyString($sRemoteObjectClass)
 				|| utils::IsNullOrEmptyString($sRemoteObjectKey)
-				|| ($sRemoteObjectKey == 0) // non-strict comparison as we might have bad surprises
 			) {
 				continue;
 			}
 
+			// 0 : Undefined ext. key (EG. non-mandatory and no value provided)
+			// < 0 : Non yet persisted object
+            /** @noinspection TypeUnsafeComparisonInspection Non-strict comparison as object ID can be string */
+			if ($sRemoteObjectKey <= 0) {
+				continue;
+			}
+
 			if (false === $oIsObjectLoadableCallback($sRemoteObjectClass, $sRemoteObjectKey)) {
 				throw new InvalidExternalKeyValueException($this, $sAttDefCode);
 			}