diff --git a/addressbook/inc/class.addressbook_merge.inc.php b/addressbook/inc/class.addressbook_merge.inc.php
index 9b59af4c0d..dd30daf847 100644
--- a/addressbook/inc/class.addressbook_merge.inc.php
+++ b/addressbook/inc/class.addressbook_merge.inc.php
@@ -45,9 +45,9 @@ class addressbook_merge extends bo_merge
 		{
 			return false;
 		}
-		if (strpos($content,'$$calendar/') !== null)
+		if (!(strpos($content,'$$calendar/') === false))
 		{
-			$replacements += $this->calendar_replacements($id,strpos($content,'$$calendar/-1/') !== null);
+			$replacements += $this->calendar_replacements($id,!(strpos($content,'$$calendar/-1/') === false));
 		}
 		return $replacements;
 	}