diff --git a/std/http/file_server.ts b/std/http/file_server.ts
index e4c8c49313..b75f9f9c14 100644
--- a/std/http/file_server.ts
+++ b/std/http/file_server.ts
@@ -322,14 +322,15 @@ function html(strings: TemplateStringsArray, ...values: unknown[]): string {
 }
 
 function normalizeURL(url: string): string {
-  let normalizedUrl = posix.normalize(url);
+  let normalizedUrl = url;
   try {
-    normalizedUrl = decodeURIComponent(normalizedUrl);
+    normalizedUrl = decodeURI(normalizedUrl);
   } catch (e) {
     if (!(e instanceof URIError)) {
       throw e;
     }
   }
+  normalizedUrl = posix.normalize(normalizedUrl);
   const startOfParams = normalizedUrl.indexOf("?");
   return startOfParams > -1
     ? normalizedUrl.slice(0, startOfParams)
diff --git a/std/http/file_server_test.ts b/std/http/file_server_test.ts
index 3368b2e15d..ca8d3b3b28 100644
--- a/std/http/file_server_test.ts
+++ b/std/http/file_server_test.ts
@@ -1,5 +1,9 @@
 // Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
-import { assert, assertEquals } from "../testing/asserts.ts";
+import {
+  assert,
+  assertEquals,
+  assertStringIncludes,
+} from "../testing/asserts.ts";
 import { BufReader } from "../io/bufio.ts";
 import { TextProtoReader } from "../textproto/mod.ts";
 import { ServerRequest } from "./server.ts";
@@ -147,6 +151,37 @@ Deno.test("serveFallback", async function (): Promise<void> {
   }
 });
 
+Deno.test("checkPathTraversal", async function (): Promise<void> {
+  await startFileServer();
+  try {
+    const res = await fetch(
+      "http://localhost:4507/../../../../../../../..",
+    );
+    assert(res.headers.has("access-control-allow-origin"));
+    assert(res.headers.has("access-control-allow-headers"));
+    assertEquals(res.status, 200);
+    const listing = await res.text();
+    assertStringIncludes(listing, "README.md");
+  } finally {
+    await killFileServer();
+  }
+});
+
+Deno.test("checkURIEncodedPathTraversal", async function (): Promise<void> {
+  await startFileServer();
+  try {
+    const res = await fetch(
+      "http://localhost:4507/%2F..%2F..%2F..%2F..%2F..%2F..%2F..%2F..",
+    );
+    assert(res.headers.has("access-control-allow-origin"));
+    assert(res.headers.has("access-control-allow-headers"));
+    assertEquals(res.status, 404);
+    const _ = await res.text();
+  } finally {
+    await killFileServer();
+  }
+});
+
 Deno.test("serveWithUnorthodoxFilename", async function (): Promise<void> {
   await startFileServer();
   try {