diff --git a/src/lib/transform-include-atrule.js b/src/lib/transform-include-atrule.js
index 2ad340f..a46fda1 100644
--- a/src/lib/transform-include-atrule.js
+++ b/src/lib/transform-include-atrule.js
@@ -62,4 +62,4 @@ const getIncludeOpts = node => {
 };
 
 // match an opening parenthesis
-const matchOpeningParen = '(';
+const matchOpeningParen = /(?<!var)\(/;
diff --git a/src/lib/transform-mixin-atrule.js b/src/lib/transform-mixin-atrule.js
index 7d9c910..bc7a5cf 100644
--- a/src/lib/transform-mixin-atrule.js
+++ b/src/lib/transform-mixin-atrule.js
@@ -40,4 +40,4 @@ const getMixinOpts = (node, opts) => {
 };
 
 // match an opening parenthesis
-const matchOpeningParen = '(';
+const matchOpeningParen = /(?<!var)\(/;