diff --git a/src/cmd/go/alldocs.go b/src/cmd/go/alldocs.go
index 2316fb9..68bad3c 100644
--- a/src/cmd/go/alldocs.go
+++ b/src/cmd/go/alldocs.go
@@ -1700,6 +1700,8 @@
 // 	GOCACHE
 // 		The directory where the go command will store cached
 // 		information for reuse in future builds.
+// 	GOMODCACHE
+// 		The directory where the go command will store downloaded modules.
 // 	GODEBUG
 // 		Enable various debugging facilities. See 'go doc runtime'
 // 		for details.
diff --git a/src/cmd/go/internal/help/helpdoc.go b/src/cmd/go/internal/help/helpdoc.go
index b937a61..e1f0521 100644
--- a/src/cmd/go/internal/help/helpdoc.go
+++ b/src/cmd/go/internal/help/helpdoc.go
@@ -493,6 +493,8 @@
 	GOCACHE
 		The directory where the go command will store cached
 		information for reuse in future builds.
+	GOMODCACHE
+		The directory where the go command will store downloaded modules.
 	GODEBUG
 		Enable various debugging facilities. See 'go doc runtime'
 		for details.