--- /dev/null
+/* @flow */
+"use strict";
+
+const _ = require("lodash");
+const hasBlock = require("../utils/hasBlock");
+
+/**
+ * Check whether a Node is a custom property set
+ */
+module.exports = function(node /*: Object*/) /*: boolean*/ {
+ const selector = _.get(node, "raws.selector.raw", node.selector);
+
+ return (
+ node.type === "rule" &&
+ hasBlock(node) &&
+ selector.slice(0, 2) === "--" &&
+ selector.slice(-1) === ":"
+ );
+};