diff --git a/js/src/jsdate.h b/js/src/jsdate.h
index 3941ea2cbae6..816487844412 100644
--- a/js/src/jsdate.h
+++ b/js/src/jsdate.h
@@ -45,15 +45,27 @@ extern JSObject *
 js_InitDateClass(JSContext *cx, JSObject *obj);
 
 /*
- *  These functions provide a C interface to the date/time object
+ * These functions provide a C interface to the date/time object
+ */
+
+/*
+ * Construct a new Date Object from a time value given in milliseconds UTC
+ * since the epoch.
  */
 extern JS_FRIEND_API(JSObject*)
 js_NewDateObjectMsec(JSContext* cx, jsdouble msec_time);
 
+/*
+ * Construct a new Date Object from an exploded local time value.
+ */
 extern JS_FRIEND_API(JSObject*)
 js_NewDateObject(JSContext* cx, int year, int mon, int mday,
 				int hour, int min, int sec);
 
+/*
+ * Detect whether the internal date value is NaN.  (Because failure is
+ * out-of-band for js_DateGet*)
+ */
 extern JS_FRIEND_API(JSBool)
 js_DateIsValid(JSContext *cx, JSObject* obj);