If @@toStringTag is not present, use the old-school Object#toString test.

Author: ljharb

index.js

@@ -1,7 +1,6 @@
 'use strict';
 
 var regexExec = RegExp.prototype.exec;
-
 var tryRegexExec = function tryRegexExec(value) {
 	try {
 		regexExec.call(value);
@@ -10,8 +9,11 @@ var tryRegexExec = function tryRegexExec(value) {
 		return false;
 	}
 };
+var toStr = Object.prototype.toString;
+var regexClass = '[object RegExp]';
+var hasToStringTag = typeof Symbol === 'function' && typeof Symbol.toStringTag === 'symbol';
 
 module.exports = function isRegex(value) {
 	if (typeof value !== 'object') { return false; }
-	return tryRegexExec(value);
+	return hasToStringTag ? tryRegexExec(value) : toStr.call(value) === regexClass;
 };

package.json

@@ -6,7 +6,7 @@
 	"license": "MIT",
 	"main": "index.js",
 	"scripts": {
-		"test": "npm run lint && node test.js && npm run coverage-quiet",
+		"test": "npm run lint && node test.js",
 		"coverage": "covert test.js",
 		"coverage-quiet": "covert test.js --quiet",
 		"lint": "jscs *.js"