Index: src/wp-admin/includes/update.php
===================================================================
--- src/wp-admin/includes/update.php	(revision 46166)
+++ src/wp-admin/includes/update.php	(working copy)
@@ -707,7 +707,7 @@
 		 * This flag is cleared whenever a successful update occurs using Core_Upgrader.
 		 */
 		$comparison = ! empty( $failed['critical'] ) ? '>=' : '>';
-		if ( version_compare( $failed['attempted'], $wp_version, $comparison ) ) {
+		if ( isset( $failed['attempted'] ) && version_compare( $failed['attempted'], $wp_version, $comparison ) ) {
 			$nag = true;
 		}
 	}