diff --git a/src/pkg/math/rand/rand.go b/src/pkg/math/rand/rand.go
index 608012a300..2157cdb465 100644
--- a/src/pkg/math/rand/rand.go
+++ b/src/pkg/math/rand/rand.go
@@ -8,6 +8,7 @@
 // Float64 and Int, use a default shared Source that produces a deterministic
 // sequence of values each time a program is run. Use the Seed function to
 // initialize the default Source if different behavior is required for each run.
+// The default Source is safe for concurrent use by multiple goroutines.
 package rand
 
 import "sync"