diff --git a/src/sync/map.go b/src/sync/map.go
index a61e2ebdd67f72..14454f191dadca 100644
--- a/src/sync/map.go
+++ b/src/sync/map.go
@@ -24,6 +24,7 @@ import (
 // contention compared to a Go map paired with a separate Mutex or RWMutex.
 //
 // The zero Map is empty and ready for use. A Map must not be copied after first use.
+// Keys in the Map are never deleted, thus they will never be garbage collected.
 type Map struct {
 	mu Mutex