diff --git a/lib/precondition.js b/lib/precondition.js
index 1781449..070beea 100644
--- a/lib/precondition.js
+++ b/lib/precondition.js
@@ -7,7 +7,7 @@ module.exports = function (iterations, keylen) {
 		throw new TypeError('Iterations not a number');
 	}
 
-	if (iterations < 0) {
+	if (iterations < 0 || !Number.isFinite(iterations)) {
 		throw new TypeError('Bad iterations');
 	}