diff --git a/lib/start-proxy-action.js b/lib/start-proxy-action.js
index a9e8e7fd9..2bdc411b7 100644
--- a/lib/start-proxy-action.js
+++ b/lib/start-proxy-action.js
@@ -119806,8 +119806,11 @@ async function cacheProxy(logger, source, filename, version) {
     throw new StartProxyError("Failed to add proxy to toolcache" /* CacheFailed */);
   }
 }
+function getProxyFilename() {
+  return process.platform === "win32" ? `${UPDATEJOB_PROXY}.exe` : UPDATEJOB_PROXY;
+}
 async function getProxyBinaryPath(logger) {
-  const proxyFileName = process.platform === "win32" ? `${UPDATEJOB_PROXY}.exe` : UPDATEJOB_PROXY;
+  const proxyFileName = getProxyFilename();
   const proxyInfo = await getDownloadUrl(logger);
   let proxyBin = toolcache.find(proxyFileName, proxyInfo.version);
   if (!proxyBin) {
diff --git a/src/start-proxy.test.ts b/src/start-proxy.test.ts
index 6cd1b2e98..f7a0dd707 100644
--- a/src/start-proxy.test.ts
+++ b/src/start-proxy.test.ts
@@ -1,3 +1,5 @@
+import * as filepath from "path";
+
 import * as core from "@actions/core";
 import * as toolcache from "@actions/tool-cache";
 import test, { ExecutionContext } from "ava";
@@ -484,7 +486,10 @@ test("getProxyBinaryPath - returns path from tool cache if available", async (t)
     const path = await startProxyExports.getProxyBinaryPath(logger);
 
     t.assert(path);
-    t.assert(path.startsWith(toolcachePath));
+    t.is(
+      path,
+      filepath.join(toolcachePath, startProxyExports.getProxyFilename()),
+    );
   });
 });
 
@@ -525,6 +530,9 @@ test("getProxyBinaryPath - downloads proxy if not in cache", async (t) => {
     t.assert(cacheDir.calledOnceWith(extractedPath));
 
     t.assert(path);
-    t.assert(path.startsWith(toolcachePath));
+    t.is(
+      path,
+      filepath.join(toolcachePath, startProxyExports.getProxyFilename()),
+    );
   });
 });
diff --git a/src/start-proxy.ts b/src/start-proxy.ts
index 94d373fa1..980eb44b6 100644
--- a/src/start-proxy.ts
+++ b/src/start-proxy.ts
@@ -486,6 +486,15 @@ export async function cacheProxy(
   }
 }
 
+/**
+ * Returns the platform-specific filename of the proxy binary.
+ */
+export function getProxyFilename() {
+  return process.platform === "win32"
+    ? `${UPDATEJOB_PROXY}.exe`
+    : UPDATEJOB_PROXY;
+}
+
 /**
  * Gets a path to the proxy binary. If possible, this function will find the proxy in the
  * runner's tool cache. Otherwise, it downloads and extracts the proxy binary,
@@ -495,8 +504,7 @@ export async function cacheProxy(
  * @returns The path to the proxy binary.
  */
 export async function getProxyBinaryPath(logger: Logger): Promise<string> {
-  const proxyFileName =
-    process.platform === "win32" ? `${UPDATEJOB_PROXY}.exe` : UPDATEJOB_PROXY;
+  const proxyFileName = getProxyFilename();
   const proxyInfo = await getDownloadUrl(logger);
 
   let proxyBin = toolcache.find(proxyFileName, proxyInfo.version);