diff --git a/src/wp-includes/l10n.php b/src/wp-includes/l10n.php
index 4f3ec8bfed..1923c8c2a2 100644
--- a/src/wp-includes/l10n.php
+++ b/src/wp-includes/l10n.php
@@ -821,7 +821,7 @@ function load_textdomain( $domain, $mofile, $locale = null ) {
 	if ( 'mo' !== $preferred_format ) {
 		array_unshift(
 			$translation_files,
-			substr_replace( $mofile, '.l10n.', - strlen( $preferred_format ) )
+			substr_replace( $mofile, ".l10n.$preferred_format", - strlen( $preferred_format ) )
 		);
 	}