diff --git a/op/op.SetRevisors.php b/op/op.SetRevisors.php
index 672cd6677..3716b0183 100644
--- a/op/op.SetRevisors.php
+++ b/op/op.SetRevisors.php
@@ -55,10 +55,12 @@ if (!is_object($content)) {
 	UI::exitError(getMLText("document_title", array("documentname" => $document->getName())),getMLText("invalid_version"));
 }
 
-if (isset($_POST["startdate"])) {
+$ts = null;
+if (!empty($_POST["startdate"])) {
 	$ts = makeTsFromDate($_POST["startdate"]);
-} else {
-	$ts = time();
+}
+if(!$ts) {
+	UI::exitError(getMLText("document_title", array("documentname" => $document->getName())),getMLText("invalid_revision_date"));
 }
 $startdate = date('Y-m-d', $ts);