diff --git a/index.js b/index.js
index 27f19b7..c089e0c 100644
--- a/index.js
+++ b/index.js
@@ -9,10 +9,11 @@
 
 module.exports = function(num) {
   if (typeof num === 'number') {
-    return num - num === 0;
+    return Number.isFinite(num);
   }
-  if (typeof num === 'string' && num.trim() !== '') {
-    return Number.isFinite ? Number.isFinite(+num) : isFinite(+num);
+    if (typeof num === 'string' && num.trim()) {
+      const parsed = Number(num)
+    return Number.isFinite(parsed);
   }
   return false;
 };