diff --git a/src/index.js b/src/index.js
index 0729afb0..9392d1fa 100644
--- a/src/index.js
+++ b/src/index.js
@@ -33,7 +33,7 @@ async function lessLoader(source) {
   if (typeof options.additionalData !== 'undefined') {
     data =
       typeof options.additionalData === 'function'
-        ? `${options.additionalData(data, this)}`
+        ? `${await options.additionalData(data, this)}`
         : `${options.additionalData}\n${data}`;
   }