diff --git a/scss/_functions.scss b/scss/_functions.scss
index 9c06603150ed..8abc31164e98 100644
--- a/scss/_functions.scss
+++ b/scss/_functions.scss
@@ -120,6 +120,14 @@
     @return $value1 + $value2;
   }
 
+  @if type-of($value1) != number {
+    $value1: unquote("(") + $value1 + unquote(")");
+  }
+
+  @if type-of($value2) != number {
+    $value2: unquote("(") + $value2 + unquote(")");
+  }
+
   @return if($return-calc == true, calc(#{$value1} + #{$value2}), $value1 + unquote(" + ") + $value2);
 }
 
@@ -140,5 +148,13 @@
     @return $value1 - $value2;
   }
 
+  @if type-of($value1) != number {
+    $value1: unquote("(") + $value1 + unquote(")");
+  }
+
+  @if type-of($value2) != number {
+    $value2: unquote("(") + $value2 + unquote(")");
+  }
+
   @return if($return-calc == true, calc(#{$value1} - #{$value2}), $value1 + unquote(" - ") + $value2);
 }