diff --git a/core/mutex.class.inc.php b/core/mutex.class.inc.php
index 8c7a7a918..82e67dd60 100644
--- a/core/mutex.class.inc.php
+++ b/core/mutex.class.inc.php
@@ -131,7 +131,11 @@ class iTopMutex
 			$this->bLocked = true;
 			self::$aAcquiredLocks[$this->sName]++;
 		}
-		return ($res === '1');
+		if (($res !== '1') && ($res !== '0'))
+		{
+			IssueLog::Error('GET_LOCK('.$this->sName.', 0) returned: '.var_export($res, true).'. Expected values are: 0, 1 or null !!');
+		}
+		return ($res !== '0');
 	}
 
 	/**