diff --git a/includes/specials/SpecialComparePages.php b/includes/specials/SpecialComparePages.php
index 5531a6dde2f..81fd92f71bd 100644
--- a/includes/specials/SpecialComparePages.php
+++ b/includes/specials/SpecialComparePages.php
@@ -130,7 +130,7 @@ class SpecialComparePages extends SpecialPage {
 	}
 
 	public function checkExistingTitle( $value, $alldata ) {
-		if ( $value === '' ) {
+		if ( $value === '' || $value === null ) {
 			return true;
 		}
 		$title = Title::newFromText( $value );
@@ -144,7 +144,7 @@ class SpecialComparePages extends SpecialPage {
 	}
 
 	public function checkExistingRevision( $value, $alldata ) {
-		if ( $value === '' ) {
+		if ( $value === '' || $value === null ) {
 			return true;
 		}
 		$revision = Revision::newFromId( $value );