diff --git a/deno_dist/utils/filepath.ts b/deno_dist/utils/filepath.ts
index 35c6159f7..efcc72b6d 100644
--- a/deno_dist/utils/filepath.ts
+++ b/deno_dist/utils/filepath.ts
@@ -1,51 +1,59 @@
+const DEFAULT_DOCUMENT = 'index.html'
+const VALID_EXTENSION_REGEX = /\.[a-zA-Z0-9]+$/
+const PARENT_DIRECTORY_REGEX = /(?:^|[\/\\])\.\.(?:$|[\/\\])/
+
 type FilePathOptions = {
   filename: string
   root?: string
   defaultDocument?: string
 }
 
-export const getFilePath = (options: FilePathOptions): string | undefined => {
-  let filename = options.filename
-  const defaultDocument = options.defaultDocument || 'index.html'
-
-  if (filename.endsWith('/')) {
-    // /top/ => /top/index.html
-    filename = filename.concat(defaultDocument)
-  } else if (!filename.match(/\.[a-zA-Z0-9]+$/)) {
-    // /top => /top/index.html
-    filename = filename.concat('/' + defaultDocument)
-  }
-
-  const path = getFilePathWithoutDefaultDocument({
-    root: options.root,
-    filename,
+/**
+ * Retrieves the file path based on the provided options.
+ * If no default document is specified, 'index.html' is appended to the path.
+ * If the filename ends with '/', the default document is appended.
+ * If the filename has no valid extension, the default document is appended.
+ * @param options - The options object containing filename, root, and defaultDocument.
+ * @returns The final file path or undefined if parent directory traversal is detected.
+ */
+export const getFilePath = ({
+  filename,
+  defaultDocument,
+  root,
+}: FilePathOptions): string | undefined => {
+  const isDefaultDocument = defaultDocument || DEFAULT_DOCUMENT
+
+  const shouldAppendDefault = filename.endsWith('/') || !filename.match(VALID_EXTENSION_REGEX)
+
+  const finalFilename = shouldAppendDefault
+    ? filename.concat('/', isDefaultDocument || DEFAULT_DOCUMENT)
+    : filename
+
+  return getFilePathWithoutDefaultDocument({
+    root,
+    filename: finalFilename,
   })
-
-  return path
 }
 
-export const getFilePathWithoutDefaultDocument = (
-  options: Omit<FilePathOptions, 'defaultDocument'>
-) => {
-  let root = options.root || ''
-  let filename = options.filename
-
-  if (/(?:^|[\/\\])\.\.(?:$|[\/\\])/.test(filename)) {
+/**
+ * Retrieves the file path without appending the default document.
+ * If parent directory traversal is detected in the filename, returns undefined.
+ * Replaces backslashes with forward slashes and removes redundant slashes.
+ * @param options The options object containing filename and root.
+ * @returns The sanitized file path.
+ */
+export const getFilePathWithoutDefaultDocument = ({
+  filename,
+  root = '',
+}: Omit<FilePathOptions, 'defaultDocument'>) => {
+  if (PARENT_DIRECTORY_REGEX.test(filename)) {
     return
   }
 
-  // /foo.html => foo.html
-  filename = filename.replace(/^\.?[\/\\]/, '')
-
-  // foo\bar.txt => foo/bar.txt
-  filename = filename.replace(/\\/, '/')
-
-  // assets/ => assets
-  root = root.replace(/\/$/, '')
+  const sanitizedFilename = filename.replace(/^\.?[\/\\]/, '').replace(/\\/, '/')
+  const sanitizedRoot = root.replace(/\/$/, '')
 
-  // ./assets/foo.html => assets/foo.html
-  let path = root ? root + '/' + filename : filename
-  path = path.replace(/^\.?\//, '')
+  const path = sanitizedRoot ? sanitizedRoot + '/' + sanitizedFilename : sanitizedFilename
 
-  return path
+  return path.replace(/^\.?\//, '')
 }
diff --git a/src/utils/filepath.test.ts b/src/utils/filepath.test.ts
index 5d6482e2d..44e3a1d2a 100644
--- a/src/utils/filepath.test.ts
+++ b/src/utils/filepath.test.ts
@@ -1,7 +1,7 @@
 import { getFilePath, getFilePathWithoutDefaultDocument } from './filepath'
 
 describe('getFilePathWithoutDefaultDocument', () => {
-  it('Should return file path correctly', async () => {
+  it('should return file path correctly without default document', () => {
     expect(getFilePathWithoutDefaultDocument({ filename: 'foo.txt' })).toBe('foo.txt')
     expect(getFilePathWithoutDefaultDocument({ filename: 'foo.txt', root: 'bar' })).toBe(
       'bar/foo.txt'
@@ -10,6 +10,7 @@ describe('getFilePathWithoutDefaultDocument', () => {
     expect(getFilePathWithoutDefaultDocument({ filename: '../foo' })).toBeUndefined()
     expect(getFilePathWithoutDefaultDocument({ filename: '/../foo' })).toBeUndefined()
     expect(getFilePathWithoutDefaultDocument({ filename: './../foo' })).toBeUndefined()
+
     expect(getFilePathWithoutDefaultDocument({ filename: 'foo..bar.txt' })).toBe('foo..bar.txt')
     expect(getFilePathWithoutDefaultDocument({ filename: '/foo..bar.txt' })).toBe('foo..bar.txt')
     expect(getFilePathWithoutDefaultDocument({ filename: './foo..bar.txt' })).toBe('foo..bar.txt')
@@ -47,9 +48,8 @@ describe('getFilePathWithoutDefaultDocument', () => {
 })
 
 describe('getFilePath', () => {
-  it('Should return file path correctly', async () => {
+  it('should return file path correctly with default document', () => {
     expect(getFilePath({ filename: 'foo' })).toBe('foo/index.html')
-
     expect(getFilePath({ filename: 'foo', root: 'bar' })).toBe('bar/foo/index.html')
 
     expect(getFilePath({ filename: 'foo', defaultDocument: 'index.txt' })).toBe('foo/index.txt')
diff --git a/src/utils/filepath.ts b/src/utils/filepath.ts
index 35c6159f7..efcc72b6d 100644
--- a/src/utils/filepath.ts
+++ b/src/utils/filepath.ts
@@ -1,51 +1,59 @@
+const DEFAULT_DOCUMENT = 'index.html'
+const VALID_EXTENSION_REGEX = /\.[a-zA-Z0-9]+$/
+const PARENT_DIRECTORY_REGEX = /(?:^|[\/\\])\.\.(?:$|[\/\\])/
+
 type FilePathOptions = {
   filename: string
   root?: string
   defaultDocument?: string
 }
 
-export const getFilePath = (options: FilePathOptions): string | undefined => {
-  let filename = options.filename
-  const defaultDocument = options.defaultDocument || 'index.html'
-
-  if (filename.endsWith('/')) {
-    // /top/ => /top/index.html
-    filename = filename.concat(defaultDocument)
-  } else if (!filename.match(/\.[a-zA-Z0-9]+$/)) {
-    // /top => /top/index.html
-    filename = filename.concat('/' + defaultDocument)
-  }
-
-  const path = getFilePathWithoutDefaultDocument({
-    root: options.root,
-    filename,
+/**
+ * Retrieves the file path based on the provided options.
+ * If no default document is specified, 'index.html' is appended to the path.
+ * If the filename ends with '/', the default document is appended.
+ * If the filename has no valid extension, the default document is appended.
+ * @param options - The options object containing filename, root, and defaultDocument.
+ * @returns The final file path or undefined if parent directory traversal is detected.
+ */
+export const getFilePath = ({
+  filename,
+  defaultDocument,
+  root,
+}: FilePathOptions): string | undefined => {
+  const isDefaultDocument = defaultDocument || DEFAULT_DOCUMENT
+
+  const shouldAppendDefault = filename.endsWith('/') || !filename.match(VALID_EXTENSION_REGEX)
+
+  const finalFilename = shouldAppendDefault
+    ? filename.concat('/', isDefaultDocument || DEFAULT_DOCUMENT)
+    : filename
+
+  return getFilePathWithoutDefaultDocument({
+    root,
+    filename: finalFilename,
   })
-
-  return path
 }
 
-export const getFilePathWithoutDefaultDocument = (
-  options: Omit<FilePathOptions, 'defaultDocument'>
-) => {
-  let root = options.root || ''
-  let filename = options.filename
-
-  if (/(?:^|[\/\\])\.\.(?:$|[\/\\])/.test(filename)) {
+/**
+ * Retrieves the file path without appending the default document.
+ * If parent directory traversal is detected in the filename, returns undefined.
+ * Replaces backslashes with forward slashes and removes redundant slashes.
+ * @param options The options object containing filename and root.
+ * @returns The sanitized file path.
+ */
+export const getFilePathWithoutDefaultDocument = ({
+  filename,
+  root = '',
+}: Omit<FilePathOptions, 'defaultDocument'>) => {
+  if (PARENT_DIRECTORY_REGEX.test(filename)) {
     return
   }
 
-  // /foo.html => foo.html
-  filename = filename.replace(/^\.?[\/\\]/, '')
-
-  // foo\bar.txt => foo/bar.txt
-  filename = filename.replace(/\\/, '/')
-
-  // assets/ => assets
-  root = root.replace(/\/$/, '')
+  const sanitizedFilename = filename.replace(/^\.?[\/\\]/, '').replace(/\\/, '/')
+  const sanitizedRoot = root.replace(/\/$/, '')
 
-  // ./assets/foo.html => assets/foo.html
-  let path = root ? root + '/' + filename : filename
-  path = path.replace(/^\.?\//, '')
+  const path = sanitizedRoot ? sanitizedRoot + '/' + sanitizedFilename : sanitizedFilename
 
-  return path
+  return path.replace(/^\.?\//, '')
 }