diff --git a/src/libcore/time.rs b/src/libcore/time.rs
index 8ebdbbd83709..807a152a2aa6 100644
--- a/src/libcore/time.rs
+++ b/src/libcore/time.rs
@@ -276,7 +276,7 @@ impl Duration {
     #[unstable(feature = "duration_nanos", issue = "0")]
     #[inline]
     pub fn as_nanos(&self) -> u128 {
-        self.secs as u128 * 1000_000_000 + self.nanos as u128
+        self.secs as u128 * NANOS_PER_SEC as u128 + self.nanos as u128
     }
 
     /// Checked `Duration` addition. Computes `self + other`, returning [`None`]