diff --git a/dist/index.js b/dist/index.js
index e59b833..24b1876 100644
--- a/dist/index.js
+++ b/dist/index.js
@@ -52347,7 +52347,7 @@ async function getInputs() {
         }
     }
     const config = {
-        version: core.getInput("version") || "1.94.2",
+        version: parseVersion(core.getInput("version") || "1.94.2"),
         resolvedVersion: "",
         arch: "",
         authKey: authKey,
@@ -52371,6 +52371,16 @@ async function getInputs() {
     }
     return config;
 }
+function parseVersion(input) {
+    if (input === versionLatest || input === versionUnstable) {
+        return input;
+    }
+    const version = input.replace(/^v/, "");
+    if (!/^\d+\.\d+\.\d+$/.test(version)) {
+        throw new Error(`Invalid version "${input}": use a version number such as 1.104.2, "latest", or "unstable".`);
+    }
+    return version;
+}
 function validateAuth(config) {
     if (!config.authKey &&
         (!config.oauthSecret || !config.tags) &&
diff --git a/src/main.ts b/src/main.ts
index 109d4c1..73fb892 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -258,7 +258,7 @@ async function getInputs(): Promise<TailscaleConfig> {
   }
 
   const config = {
-    version: core.getInput("version") || "1.94.2",
+    version: parseVersion(core.getInput("version") || "1.94.2"),
     resolvedVersion: "",
     arch: "",
     authKey: authKey,
@@ -287,6 +287,19 @@ async function getInputs(): Promise<TailscaleConfig> {
   return config;
 }
 
+function parseVersion(input: string): string {
+  if (input === versionLatest || input === versionUnstable) {
+    return input;
+  }
+  const version = input.replace(/^v/, "");
+  if (!/^\d+\.\d+\.\d+$/.test(version)) {
+    throw new Error(
+      `Invalid version "${input}": use a version number such as 1.104.2, "latest", or "unstable".`,
+    );
+  }
+  return version;
+}
+
 function validateAuth(config: TailscaleConfig): void {
   if (
     !config.authKey &&