diff --git a/src/wp-includes/functions.php b/src/wp-includes/functions.php
index c834a01ef4..8835ecfec4 100644
--- a/src/wp-includes/functions.php
+++ b/src/wp-includes/functions.php
@@ -3300,6 +3300,13 @@ function get_allowed_mime_types( $user = null ) {
 		unset( $t['htm|html'], $t['js'] );
 	}
 
+	// Add WebP if the server supports it.
+	unset( $t['webp'] );
+
+	if ( wp_image_editor_supports( array( 'mime_type' => 'image/webp' ) ) ) {
+		$t['webp'] = 'image/webp';
+	}
+
 	/**
 	 * Filters list of allowed mime types and file extensions.
 	 *
diff --git a/src/wp-includes/script-loader.php b/src/wp-includes/script-loader.php
index 2e1e6668cd..c7a6963f73 100644
--- a/src/wp-includes/script-loader.php
+++ b/src/wp-includes/script-loader.php
@@ -851,7 +851,7 @@ function wp_default_scripts( $scripts ) {
 		/* translators: %s: File name. */
 		'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'          => __( 'Sorry, this file type is not permitted for security reasons.' ),
+		'invalid_filetype'          => __( 'Sorry, this file type is not supported.' ),
 		'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.' ),