diff --git src/wp-includes/functions.php src/wp-includes/functions.php
index be01132..c908287 100644
--- src/wp-includes/functions.php
+++ src/wp-includes/functions.php
@@ -1993,7 +1993,17 @@ function wp_unique_filename( $dir, $filename, $unique_filename_callback = null )
 		}
 	}
 
-	return $filename;
+	/**
+	 * Filter the filename.
+	 *
+	 * @since 4.5.0
+	 *
+	 * @param  string   $filename                 File name.
+	 * @param  string   $ext                      File extension.
+	 * @param  string   $dir                      Directory.
+	 * @param  callable $unique_filename_callback Callback. Default null.
+	 */
+	return apply_filters( 'wp_unique_filename', $filename, $ext, $dir, $unique_filename_callback );
 }
 
 /**