diff --git a/doc/play/pi.go b/doc/play/pi.go
index f2f5dca748..f61884e888 100644
--- a/doc/play/pi.go
+++ b/doc/play/pi.go
@@ -1,5 +1,5 @@
 // Concurrent computation of pi.
-// See http://goo.gl/ZuTZM.
+// See https://goo.gl/la6Kli.
 //
 // This demonstrates Go's ability to handle
 // large numbers of concurrent processes.