diff --git a/lodash.js b/lodash.js
index 909d6ebef..d53f28bc2 100644
--- a/lodash.js
+++ b/lodash.js
@@ -12018,7 +12018,7 @@
         return NAN;
       }
       if (isObject(value)) {
-        var other = isFunction(value.valueOf) ? value.valueOf() : value;
+        var other = typeof value.valueOf == 'function' ? value.valueOf() : value;
         value = isObject(other) ? (other + '') : other;
       }
       if (typeof value != 'string') {