diff --git a/theme/boost/lib.php b/theme/boost/lib.php
index 7e98100f6d8..6cc398d535e 100644
--- a/theme/boost/lib.php
+++ b/theme/boost/lib.php
@@ -135,7 +135,7 @@ function theme_boost_get_precompiled_css() {
  * Get SCSS to prepend.
  *
  * @param theme_config $theme The theme config object.
- * @return array
+ * @return string
  */
 function theme_boost_get_pre_scss($theme) {
     global $CFG;