diff --git a/phpBB/styles/prosilver/template/jumpbox.html b/phpBB/styles/prosilver/template/jumpbox.html
index f7b4fca609..1029627561 100644
--- a/phpBB/styles/prosilver/template/jumpbox.html
+++ b/phpBB/styles/prosilver/template/jumpbox.html
@@ -10,7 +10,7 @@
 <!-- ENDIF -->
 
 <!-- IF S_DISPLAY_JUMPBOX -->
-	<form method="post" id="jumpbox" action="{S_JUMPBOX_ACTION}" onsubmit="if(document.jumpbox.f.value == -1){return false;}">
+	<form method="post" id="jumpbox" action="{S_JUMPBOX_ACTION}" onsubmit="if(this.f.value == -1){return false;}">
 
 	<!-- IF $CUSTOM_FIELDSET_CLASS -->
 		<fieldset class="{$CUSTOM_FIELDSET_CLASS}">