diff --git a/src/wp-includes/widgets.php b/src/wp-includes/widgets.php
index 9aca45163d..877357606b 100644
--- a/src/wp-includes/widgets.php
+++ b/src/wp-includes/widgets.php
@@ -1565,7 +1565,7 @@ function wp_widget_rss_output( $rss, $args = array() ) {
 	echo '<ul>';
 	foreach ( $rss->get_items( 0, $items ) as $item ) {
 		$link = $item->get_link();
-		while ( stristr( $link, 'http' ) !== $link ) {
+		while ( ! empty( $link ) && stristr( $link, 'http' ) !== $link ) {
 			$link = substr( $link, 1 );
 		}
 		$link = esc_url( strip_tags( $link ) );
diff --git a/src/wp-includes/widgets/class-wp-widget-rss.php b/src/wp-includes/widgets/class-wp-widget-rss.php
index 332ba98d88..b38a8a17c3 100644
--- a/src/wp-includes/widgets/class-wp-widget-rss.php
+++ b/src/wp-includes/widgets/class-wp-widget-rss.php
@@ -50,7 +50,7 @@ class WP_Widget_RSS extends WP_Widget {
 		}
 
 		$url = ! empty( $instance['url'] ) ? $instance['url'] : '';
-		while ( stristr( $url, 'http' ) !== $url ) {
+		while ( ! empty( $url ) && stristr( $url, 'http' ) !== $url ) {
 			$url = substr( $url, 1 );
 		}
 
@@ -74,7 +74,7 @@ class WP_Widget_RSS extends WP_Widget {
 				$title = strip_tags( $rss->get_title() );
 			}
 			$link = strip_tags( $rss->get_permalink() );
-			while ( stristr( $link, 'http' ) !== $link ) {
+			while ( ! empty( $link ) && stristr( $link, 'http' ) !== $link ) {
 				$link = substr( $link, 1 );
 			}
 		}