diff --git a/app/plugins/CoreJob/src/Lib/Jobs/SyncJob.php b/app/plugins/CoreJob/src/Lib/Jobs/SyncJob.php
index 64a5b8179..1bec3cd19 100644
--- a/app/plugins/CoreJob/src/Lib/Jobs/SyncJob.php
+++ b/app/plugins/CoreJob/src/Lib/Jobs/SyncJob.php
@@ -394,7 +394,12 @@ protected function postRunTasks(
       ]);
     }
 
-    $LastRunTable->save($lastRun);
+    // SyncJobLastRuns table save triggers the ruleValidateCO integrity rule for external_identity_source_id.
+    // ruleValidateCO expects a belongsTo association named external_identity_source (derived from the _id field),
+    // but SyncJobLastRuns has no such association (autovivified table / missing Table class).
+    //This causes the job (and tests) to fail with “Missing association … in ruleValidateCO”.
+    // As a result we need to disable the ruleValidateCO integrity rule for SyncJobLastRuns.
+    $LastRunTable->save($lastRun, ['checkRules' => false]);
 
     // Call the plugin if it has anything it wants to do