diff --git a/sass/font-awesome.scss b/sass/font-awesome.scss
index 2faacaf54..2a6d10e4b 100644
--- a/sass/font-awesome.scss
+++ b/sass/font-awesome.scss
@@ -55,7 +55,7 @@ a [class*=" icon-"] {
 /* makes the font 33% larger relative to the icon container */
 .icon-large:before {
   vertical-align: middle;
-  font-size: 4/3em;
+  font-size: #{(4/3)}em;
 }
 
 .btn, .nav-tabs {