diff --git a/content/handlers/javascript/duktape/Window.bnd b/content/handlers/javascript/duktape/Window.bnd
index 731b2a335..db588c09c 100644
--- a/content/handlers/javascript/duktape/Window.bnd
+++ b/content/handlers/javascript/duktape/Window.bnd
@@ -264,6 +264,7 @@ prototype Window()
 	EXPOSE(encodeURI);
 	EXPOSE(encodeURIComponent);
 	EXPOSE(NaN);
+	EXPOSE(isNaN);
 #undef EXPOSE
 	/* Add s3kr1t method to close the compartment */
 	duk_dup(ctx, 0);