diff --git a/go.mod b/go.mod
index 74f9af0..e54520a 100644
--- a/go.mod
+++ b/go.mod
@@ -2,4 +2,7 @@
 
 go 1.9
 
-require github.com/google/go-cmp v0.3.0
+require (
+	github.com/golang/protobuf v1.4.0-rc.1
+	github.com/google/go-cmp v0.3.1
+)
diff --git a/go.sum b/go.sum
index 7e5f1f7..6408613 100644
--- a/go.sum
+++ b/go.sum
@@ -1,2 +1,7 @@
+github.com/golang/protobuf v1.4.0-rc.1 h1:axiiuL94A9bpjZyKcirx5U62av32UORcixjrwLdzvMo=
+github.com/golang/protobuf v1.4.0-rc.1/go.mod h1:ceaxUfeHdC40wWswd/P6IGgMaK3YpKi5j83Wpe3EHw8=
 github.com/google/go-cmp v0.3.0 h1:crn/baboCvb5fXaQ0IJ1SGTsTVrWpDsCWC8EGETZijY=
 github.com/google/go-cmp v0.3.0/go.mod h1:8QqcDgzrUqlUb/G2PQTWiueGozuR1884gddMywk6iLU=
+github.com/google/go-cmp v0.3.1 h1:Xye71clBPdm5HgqGwUkwhbynsUJZhDbS20FvLhQ2izg=
+github.com/google/go-cmp v0.3.1/go.mod h1:8QqcDgzrUqlUb/G2PQTWiueGozuR1884gddMywk6iLU=
+google.golang.org/protobuf v0.0.0-20200109180630-ec00e32a8dfd/go.mod h1:DFci5gLYBciE7Vtevhsrf46CRTquxDuWsQurQQe4oz8=
diff --git a/internal/depv1/depv1.go b/internal/depv1/depv1.go
new file mode 100644
index 0000000..01d81f0
--- /dev/null
+++ b/internal/depv1/depv1.go
@@ -0,0 +1,14 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package depv1 exists to depend on github.com/golang/protobuf.
+//
+// We include this dependency to ensure that any program using
+// APIv2 also uses a sufficiently new version of APIv1. At some
+// point in the future when old versions of APIv1 are no longer
+// of concern, we may drop this dependency.
+package depv1
+
+// TODO: Delete this dependency when it no longer serves a purpose.
+import _ "github.com/golang/protobuf/proto"