diff --git a/go.mod b/go.mod
index 4f4b20e9090..850cab54f4e 100644
--- a/go.mod
+++ b/go.mod
@@ -1,3 +1,6 @@
 module golang.org/x/tools
 
-require golang.org/x/net v0.0.0-20190311183353-d8887717615a
+require (
+	golang.org/x/net v0.0.0-20190311183353-d8887717615a
+	golang.org/x/sync v0.0.0-20190423024810-112230192c58
+)
diff --git a/go.sum b/go.sum
index ffedec01023..4a6c3017839 100644
--- a/go.sum
+++ b/go.sum
@@ -1,5 +1,7 @@
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
 golang.org/x/net v0.0.0-20190311183353-d8887717615a h1:oWX7TPOiFAMXLq8o0ikBYfCJVlRHBcsciT5bXOrH628=
 golang.org/x/net v0.0.0-20190311183353-d8887717615a/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
+golang.org/x/sync v0.0.0-20190423024810-112230192c58 h1:8gQV6CLnAEikrhgkHFbMAEhagSSnXWGV915qUMm9mrU=
+golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=