diff --git a/sass/_helpers.scss b/sass/_helpers.scss
index c79658b..94f9e38 100644
--- a/sass/_helpers.scss
+++ b/sass/_helpers.scss
@@ -9,7 +9,7 @@
 /**
  * Fixed width */
 .#{$keyrune_prefix}.#{$keyrune_prefix}-fw {
-    width: calc(18em / #{$keyrune_font_size / ($keyrune_font_size * 0 + 1)});
+    width: calc(18em / #{math.div($keyrune_font_size, $keyrune_font_size * 0 + 1)});
     text-align: center;
 }
 
@@ -105,4 +105,4 @@
         color: #000;
     }
 
-}
\ No newline at end of file
+}
diff --git a/sass/_variables.scss b/sass/_variables.scss
index bab40ac..5ba4b01 100644
--- a/sass/_variables.scss
+++ b/sass/_variables.scss
@@ -10,7 +10,7 @@ $keyrune_font_variant: normal !default;
 $keyrune_font_weight: normal !default;
 $keyrune_font_size:  14px !default;
 $keyrune_font_face: 'Keyrune' !default;
-$keyrune_font: $keyrune_font_style $keyrune_font_variant $keyrune_font_weight $keyrune_font_size/1 $keyrune_font_face !default;
+$keyrune_font: $keyrune_font_style $keyrune_font_variant $keyrune_font_weight calc($keyrune_font_size/1) $keyrune_font_face !default;
 $keyrune_prefix: 'ss' !default;
 $keyrune_default_content: "\e684" !default;
 $keyrune_background_clip: text !default;
@@ -486,4 +486,4 @@ $keyrune_sets: (
 // display glyph correctly
 @function ss-content($glyph) {
     @return unquote("\"#{$glyph}\"");
-}
\ No newline at end of file
+}