diff --git a/functions/functions.php b/functions/functions.php
index 78278a1..750d41a 100644
--- a/functions/functions.php
+++ b/functions/functions.php
@@ -126,7 +126,7 @@ function get_last_value(mysqli $db, string $table, $date): float
     return floatval($data['last_value']) / 1000;
 }
 
-function get_production_values_for_month(mysqli $db, string $table, $date)
+function get_production_values_for_month(mysqli $db, string $table, $date): array
 {
     $value_query = 'SELECT date, production_og, production_eg FROM ' . $table . ' WHERE date LIKE "' . $date . '%" ORDER BY date ASC;';
     $value_result = $db->query($value_query);