diff --git a/go.mod b/go.mod
index cadaefe..3dda8e3 100644
--- a/go.mod
+++ b/go.mod
@@ -2,4 +2,7 @@
 
 go 1.9
 
-require github.com/google/go-cmp v0.5.5
+require (
+	github.com/golang/protobuf v1.5.0
+	github.com/google/go-cmp v0.5.5
+)
diff --git a/go.sum b/go.sum
index 0a5f3e0..6ba6984 100644
--- a/go.sum
+++ b/go.sum
@@ -1,4 +1,7 @@
+github.com/golang/protobuf v1.5.0 h1:LUVKkCeviFUMKqHa4tXIIij/lbhnMbP7Fn5wKdKkRh4=
+github.com/golang/protobuf v1.5.0/go.mod h1:FsONVRAS9T7sI+LIUmWTfcYkHO4aIWwzhcaSAoJOfIk=
 github.com/google/go-cmp v0.5.5 h1:Khx7svrCpmxxtHBq5j2mp/xVjsi8hQMfNLvJFAlrGgU=
 github.com/google/go-cmp v0.5.5/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
 golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543 h1:E7g+9GITq07hpfrRu66IVDexMakfv52eLZ2CXBWiKr4=
 golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
+google.golang.org/protobuf v1.26.0-rc.1/go.mod h1:jlhhOSvTdKEhbULTjvd4ARK9grFBp09yW+WbY/TyQbw=
diff --git a/internal/weakdeps/weakdeps.go b/internal/weakdeps/weakdeps.go
index 657dbe9..59b3475 100644
--- a/internal/weakdeps/weakdeps.go
+++ b/internal/weakdeps/weakdeps.go
@@ -7,8 +7,8 @@
 package weakdeps
 
 import (
-// Ensure that any program using "github.com/golang/protobuf"
-// uses a version that wraps this module so that there is a
-// unified view on what protobuf types are globally registered.
-// _ "github.com/golang/protobuf/proto" // TODO: add this back
+	// Ensure that any program using "github.com/golang/protobuf"
+	// uses a version that wraps this module so that there is a
+	// unified view on what protobuf types are globally registered.
+	_ "github.com/golang/protobuf/proto"
 )