diff --git a/wp-includes/class-walker-category.php b/wp-includes/class-walker-category.php
index 6df6431b6b..7b13264b95 100644
--- a/wp-includes/class-walker-category.php
+++ b/wp-includes/class-walker-category.php
@@ -204,8 +204,9 @@ class Walker_Category extends Walker {
 			 * @param array  $args        An array of wp_list_categories() arguments.
 			 */
 			$css_classes = implode( ' ', apply_filters( 'category_css_class', $css_classes, $category, $depth, $args ) );
+			$css_classes = $css_classes ? ' class="' . esc_attr( $css_classes ) . '"' : '';
 
-			$output .= ' class="' . $css_classes . '"';
+			$output .= $css_classes;
 			$output .= ">$link\n";
 		} elseif ( isset( $args['separator'] ) ) {
 			$output .= "\t$link" . $args['separator'] . "\n";
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 94638ed237..26589f5cd3 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.1-alpha-44413';
+$wp_version = '5.1-alpha-44414';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.