diff --git a/src/version.ts b/src/version.ts
index 950d6b7..db47935 100644
--- a/src/version.ts
+++ b/src/version.ts
@@ -2,6 +2,19 @@ import { readFileSync } from "node:fs";
 import { dirname, join } from "node:path";
 import { fileURLToPath } from "node:url";
 
+/** Read and validate the package.json version string. */
+export function readVersionFromPackageJson(packageJsonPath: string): string {
+  const pkg = JSON.parse(
+    readFileSync(packageJsonPath, "utf8"),
+  ) as { version?: unknown };
+
+  if (typeof pkg.version !== "string" || pkg.version.trim().length === 0) {
+    throw new Error("package.json is missing a valid version field.");
+  }
+
+  return pkg.version;
+}
+
 /**
  * CLI version, read from package.json at runtime so it can never drift from the
  * published version (see #48 — this used to be a hard-coded literal that fell
@@ -15,8 +28,5 @@ import { fileURLToPath } from "node:url";
  * plain runtime read instead of a copied asset.
  */
 const here = dirname(fileURLToPath(import.meta.url));
-const pkg = JSON.parse(
-  readFileSync(join(here, "..", "package.json"), "utf8"),
-) as { version: string };
 
-export const VERSION = pkg.version;
+export const VERSION = readVersionFromPackageJson(join(here, "..", "package.json"));
diff --git a/test/version.test.ts b/test/version.test.ts
new file mode 100644
index 0000000..690bd9b
--- /dev/null
+++ b/test/version.test.ts
@@ -0,0 +1,55 @@
+import { afterEach, describe, expect, it } from "vitest";
+import { mkdtempSync, readFileSync, rmSync, writeFileSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { readVersionFromPackageJson, VERSION } from "../src/version.js";
+
+const packageJson = JSON.parse(readFileSync(new URL("../package.json", import.meta.url), "utf8")) as {
+  version: string;
+};
+
+const tmpDirs: string[] = [];
+
+function writePackageJson(contents: unknown): string {
+  const tmpDir = mkdtempSync(join(tmpdir(), "mex-version-"));
+  tmpDirs.push(tmpDir);
+  const packageJsonPath = join(tmpDir, "package.json");
+  writeFileSync(packageJsonPath, JSON.stringify(contents));
+  return packageJsonPath;
+}
+
+afterEach(() => {
+  while (tmpDirs.length > 0) {
+    const tmpDir = tmpDirs.pop();
+    if (!tmpDir) continue;
+    rmSync(tmpDir, { recursive: true, force: true });
+  }
+});
+
+describe("version metadata", () => {
+  it("exports the root package.json version", () => {
+    expect(VERSION).toBe(packageJson.version);
+  });
+
+  it("reads a valid package version", () => {
+    const packageJsonPath = writePackageJson({ version: "1.2.3" });
+
+    expect(readVersionFromPackageJson(packageJsonPath)).toBe("1.2.3");
+  });
+
+  it("rejects missing, empty, or non-string versions", () => {
+    for (const contents of [
+      {},
+      { version: "" },
+      { version: "   " },
+      { version: 1 },
+      { version: null },
+    ]) {
+      const packageJsonPath = writePackageJson(contents);
+
+      expect(() => readVersionFromPackageJson(packageJsonPath)).toThrow(
+        "package.json is missing a valid version field.",
+      );
+    }
+  });
+});