diff --git a/less/mixins.less b/less/mixins.less
index 0074e89241..2493a6151e 100644
--- a/less/mixins.less
+++ b/less/mixins.less
@@ -302,7 +302,7 @@
 // Opacity
 .opacity(@opacity: 100) {
   opacity: @opacity / 100;
-   filter: ~"alpha(opacity=@{opacity})";
+  filter: ~"alpha(opacity=@{opacity})";
 }