diff --git a/wp-includes/class-wp-customize-manager.php b/wp-includes/class-wp-customize-manager.php
index f96a220349..c701364149 100644
--- a/wp-includes/class-wp-customize-manager.php
+++ b/wp-includes/class-wp-customize-manager.php
@@ -928,8 +928,12 @@ final class WP_Customize_Manager {
 
 					// Find the max widget number for this type.
 					$widget_numbers = array_keys( $settings );
-					$widget_numbers[] = 1;
-					$max_widget_numbers[ $id_base ] = call_user_func_array( 'max', $widget_numbers );
+					if ( count( $widget_numbers ) > 0 ) {
+						$widget_numbers[] = 1;
+						$max_widget_numbers[ $id_base ] = call_user_func_array( 'max', $widget_numbers );
+					} else {
+						$max_widget_numbers[ $id_base ] = 1;
+					}
 				}
 				$max_widget_numbers[ $id_base ] += 1;
 
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 6b8d8530fe..5bae15fa8b 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.7-beta1-39099';
+$wp_version = '4.7-beta1-39100';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.