diff --git a/index.js b/index.js
index 5b44368..d3d2d87 100644
--- a/index.js
+++ b/index.js
@@ -1,32 +1,14 @@
 'use strict';
 
-var $Map = typeof Map === 'function' && Map.prototype ? Map : null;
-var $Set = typeof Set === 'function' && Set.prototype ? Set : null;
+var $mapHas = typeof Map === 'function' && Map.prototype && Map.prototype.has;
+var $setHas = typeof Set === 'function' && Set.prototype && Set.prototype.has;
 
-if (!$Map) {
-	// eslint-disable-next-line no-unused-vars
-	module.exports = function isMap(x) {
-		// `Map` is not present in this environment.
-		return false;
-	};
-	return;
-}
-
-var $mapHas = $Map ? Map.prototype.has : null;
-var $setHas = $Set ? Set.prototype.has : null;
-if (!$mapHas) {
-	// eslint-disable-next-line no-unused-vars
-	module.exports = function isMap(x) {
-		// `Map` does not have a `has` method
-		return false;
-	};
-	return;
-}
-
-module.exports = function isMap(x) {
-	if (!x || typeof x !== 'object') {
+module.exports = function isSet(x) {
+	if (!$mapHas || !x || typeof x !== 'object') {
+		// `Set` is either not present in this environment or does not have a `has` method, or the argument is of an incorrect type
 		return false;
 	}
+
 	try {
 		$mapHas.call(x);
 		if ($setHas) {
@@ -36,7 +18,8 @@ module.exports = function isMap(x) {
 				return true;
 			}
 		}
-		return x instanceof $Map; // core-js workaround, pre-v2.5.0
+		return x instanceof Map; // core-js workaround, pre-v2.5.0
 	} catch (e) {}
+
 	return false;
 };