diff --git a/src/pkg/time/sleep.go b/src/pkg/time/sleep.go
index 591fa27b09..4f55bebe62 100644
--- a/src/pkg/time/sleep.go
+++ b/src/pkg/time/sleep.go
@@ -4,7 +4,8 @@
 
 package time
 
-// Sleep pauses the current goroutine for the duration d.
+// Sleep pauses the current goroutine for at least the duration d.
+// A negative or zero duration causes Sleep to return immediately.
 func Sleep(d Duration)
 
 func nano() int64 {