diff --git a/runtime/protos/version_test.go b/runtime/protos/version_test.go
new file mode 100644
index 000000000..a73203d73
--- /dev/null
+++ b/runtime/protos/version_test.go
@@ -0,0 +1,52 @@
+// Copyright 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package protos
+
+import (
+	"crypto/sha256"
+	"fmt"
+	"io"
+	"os"
+	"testing"
+)
+
+// TestDeployerVersion is designed to make it hard to forget to update the
+// deployer API version when changes are made to the deployer API. Concretely,
+// TestDeployerVersion detects any changes to runtime.proto. If the file does
+// change, the test fails and reminds you to update the deployer API version.
+//
+// This is tedious, but deployer API changes should be rare and should be
+// increasingly rare as time goes on. Plus, forgetting to update the deployer
+// API version can be very annoying to users.
+func TestDeployerVersion(t *testing.T) {
+	// Compute the SHA-256 hash of runtime.proto.
+	f, err := os.Open("runtime.proto")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer f.Close()
+
+	h := sha256.New()
+	if _, err := io.Copy(h, f); err != nil {
+		t.Fatal(err)
+	}
+	got := fmt.Sprintf("%x", h.Sum(nil))
+
+	// If runtime.proto has changed, the deployer API version may need updating.
+	const want = "49de43a1ddf1294bdba8810b300ccd0383dcc9df66e5511a21992c8ea53e5007"
+	if got != want {
+		t.Fatalf(`Unexpected SHA-256 hash of runtime.proto: got %s, want %s. If this change is meaningful, REMEMBER TO UPDATE THE DEPLOYER API VERSION in runtime/version/version.go.`, got, want)
+	}
+}