diff --git a/application/Espo/Core/FieldProcessing/Relation/LinkMultipleSaver.php b/application/Espo/Core/FieldProcessing/Relation/LinkMultipleSaver.php
index b087e374aa..45586f0fb7 100644
--- a/application/Espo/Core/FieldProcessing/Relation/LinkMultipleSaver.php
+++ b/application/Espo/Core/FieldProcessing/Relation/LinkMultipleSaver.php
@@ -205,6 +205,10 @@ class LinkMultipleSaver
                 if (!is_string($id)) {
                     throw new RuntimeException("Non-string ID in link-multiple.");
                 }
+
+                if ($id === '') {
+                    throw new RuntimeException("An entity ID value in link-multiple.");
+                }
             }
         }