diff --git a/framework/core/less/forum/Composer.less b/framework/core/less/forum/Composer.less
index 9b3a5dd0c..32e79bfc4 100644
--- a/framework/core/less/forum/Composer.less
+++ b/framework/core/less/forum/Composer.less
@@ -198,7 +198,7 @@
       background: @body-bg;
     }
     &.active:not(.fullScreen) {
-      .box-shadow(0 0 0 2px @primary-color, 0 2px 6px @shadow-color);
+      .box-shadow(~"0 0 0 2px @{primary-color}, 0 2px 6px @{shadow-color}");
     }
     &.fullScreen {
       position: fixed;