diff --git a/wp-includes/functions.php b/wp-includes/functions.php
index 2ee2be8a90..00f9d264b9 100644
--- a/wp-includes/functions.php
+++ b/wp-includes/functions.php
@@ -2139,7 +2139,7 @@ function wp_upload_bits( $name, $deprecated, $bits, $time = null ) {
 
 	$wp_filetype = wp_check_filetype( $name );
 	if ( ! $wp_filetype['ext'] && ! current_user_can( 'unfiltered_upload' ) )
-		return array( 'error' => __( 'Invalid file type' ) );
+		return array( 'error' => __( 'Sorry, this file type is not permitted for security reasons.' ) );
 
 	$upload = wp_upload_dir( $time );
 
diff --git a/wp-includes/script-loader.php b/wp-includes/script-loader.php
index b9b2bdbcac..7c571070f6 100644
--- a/wp-includes/script-loader.php
+++ b/wp-includes/script-loader.php
@@ -280,7 +280,7 @@ function wp_default_scripts( &$scripts ) {
 		'queue_limit_exceeded' => __('You have attempted to queue too many files.'),
 		'file_exceeds_size_limit' => __('%s exceeds the maximum upload size for this site.'),
 		'zero_byte_file' => __('This file is empty. Please try another.'),
-		'invalid_filetype' => __('This file type is not allowed. Please try another.'),
+		'invalid_filetype' => __('Sorry, this file type is not permitted for security reasons.'),
 		'not_an_image' => __('This file is not an image. Please try another.'),
 		'image_memory_exceeded' => __('Memory exceeded. Please try another smaller file.'),
 		'image_dimensions_exceeded' => __('This is larger than the maximum size. Please try another.'),
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 989219245c..76d1bf3257 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.8-alpha-39890';
+$wp_version = '4.8-alpha-39891';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.