diff --git a/wp-includes/class-wp-image-editor-imagick.php b/wp-includes/class-wp-image-editor-imagick.php
index 6370a53c2a..3e35775e7e 100644
--- a/wp-includes/class-wp-image-editor-imagick.php
+++ b/wp-includes/class-wp-image-editor-imagick.php
@@ -143,7 +143,7 @@ class WP_Image_Editor_Imagick extends WP_Image_Editor {
 	 * @param string $mime_type
 	 * @return boolean
 	 */
-	public static function supports_mime_type( $mime_type = null ) {
+	public static function supports_mime_type( $mime_type ) {
 		if ( ! $mime_type )
 			return false;