diff --git a/js/src/jscntxt.h b/js/src/jscntxt.h
index 0aafa9f3386e..90db8159c10a 100644
--- a/js/src/jscntxt.h
+++ b/js/src/jscntxt.h
@@ -117,7 +117,7 @@ struct JSRuntime {
 #endif
 };
 
-#ifdef va_start
+#ifdef JS_ARGUMENT_FORMATTER_DEFINED
 /*
  * Linked list mapping format strings for JS_{Convert,Push}Arguments{,VA} to
  * formatter functions.  Elements are sorted in non-increasing format string