diff --git a/src/cljs/cljs/reader.cljs b/src/cljs/cljs/reader.cljs
index a43245b..4d68d20 100644
--- a/src/cljs/cljs/reader.cljs
+++ b/src/cljs/cljs/reader.cljs
@@ -468,6 +468,11 @@ nil if the end of stream has been reached")
     (fn [month leap-year?]
       (get (if leap-year? dim-leap dim-norm) month))))
 
+(defn- drop-nanos [num]
+  (if (> num 999)
+    999 
+    num))
+
 (def ^:private parse-and-validate-timestamp
   (let [timestamp #"(\d\d\d\d)(?:-(\d\d)(?:-(\d\d)(?:[T](\d\d)(?::(\d\d)(?::(\d\d)(?:[.](\d+))?)?)?)?)?)?(?:[Z]|([-+])(\d\d):(\d\d))?"
         check (fn [low n high msg]
@@ -491,7 +496,7 @@ nil if the end of stream has been reached")
            (if-not hours 0         (check 0 h 23 "timestamp hour field must be in range 0..23"))
            (if-not minutes 0       (check 0 m 59 "timestamp minute field must be in range 0..59"))
            (if-not seconds 0       (check 0 s (if (= m 59) 60 59) "timestamp second field must be in range 0..60"))
-           (if-not milliseconds 0  (check 0 ms 999 "timestamp millisecond field must be in range 0..999"))
+           (if-not milliseconds 0  (drop-nanos (check 0 ms 999999999 "timestamp millisecond field must be in range 0..999999999999")))
            offset])))))
 
 (defn parse-timestamp