diff --git a/src/url.ts b/src/url.ts
index c600e47..7a3de3e 100644
--- a/src/url.ts
+++ b/src/url.ts
@@ -58,7 +58,7 @@ for (let c = 0x61; c <= 0x7a; c++) {
   safeHostChar[c] = 1
 }
 ;(() => {
-  const chars = '.-_'
+  const chars = '.-_:'
   for (let i = 0; i < chars.length; i++) {
     safeHostChar[chars.charCodeAt(i)] = 1
   }
@@ -74,6 +74,31 @@ export const buildUrl = (scheme: string, host: string, incomingUrl: string) => {
       needsHostValidationByURL = true
       break
     }
+    if (c === 0x3a) {
+      // ':'
+      i++
+      const firstDigit = host.charCodeAt(i)
+
+      // if the number starts with 1-9 and ranges from 1000-59999, then there is no need for normalization, so proceed
+      if (
+        firstDigit < 0x31 ||
+        firstDigit > 0x39 ||
+        i + 4 > len ||
+        i + (firstDigit < 0x36 ? 5 : 4) < len
+      ) {
+        needsHostValidationByURL = true
+        break
+      }
+      for (; i < len; i++) {
+        const c = host.charCodeAt(i)
+        if (c < 0x30 || c > 0x39) {
+          needsHostValidationByURL = true
+          break
+        }
+      }
+
+      // valid port number
+    }
   }
 
   if (needsHostValidationByURL) {
diff --git a/test/url.test.ts b/test/url.test.ts
index e1aeffc..38ef76d 100644
--- a/test/url.test.ts
+++ b/test/url.test.ts
@@ -18,41 +18,47 @@ describe('buildUrl', () => {
 
   describe('URL normalization', () => {
     test.each([
-      ['[::1]', '/foo.txt'],
-      ['[::1]:8080', '/foo.txt'],
-      ['localhost', '/'],
-      ['localhost', '/foo/bar/baz'],
-      ['localhost', '/foo_bar'],
-      ['localhost', '/foo//bar'],
-      ['localhost', '/static/%2e%2e/foo.txt'],
-      ['localhost', '/static\\..\\foo.txt'],
-      ['localhost', '/..'],
-      ['localhost', '/foo/.'],
-      ['localhost', '/foo/bar/..'],
-      ['localhost', '/a/b/../../c'],
-      ['localhost', '/a/../../../b'],
-      ['localhost', '/a/b/c/../../../'],
-      ['localhost', '/./foo.txt'],
-      ['localhost', '/foo/../bar.txt'],
-      ['localhost', '/a/./b/../c?q=%2E%2E#hash'],
-      ['localhost', '/foo/%2E/bar/../baz'],
-      ['localhost', '/hello%20world'],
-      ['localhost', '/foo%23bar'],
-      ['localhost', '/foo"bar'],
-      ['localhost', '/%2e%2E/foo'],
-      ['localhost', '/caf%C3%A9'],
-      ['localhost', '/foo%2fbar/..//baz'],
-      ['localhost', '/foo?q=../bar'],
-      ['localhost', '/path?q=hello%20world'],
-      ['localhost', '/file.txt'],
-      ['localhost', ''],
-      ['LOCALHOST', '/foo.txt'],
-      ['LOCALHOST:80', '/foo.txt'],
-      ['LOCALHOST:443', '/foo.txt'],
-      ['LOCALHOST:8080', '/foo.txt'],
-      ['Localhost:3000', '/foo.txt'],
-    ])('Should normalize %s to %s', async (host, url) => {
-      expect(buildUrl('http', host, url)).toBe(new URL(url, `http://${host}`).href)
+      ['https', '[::1]', '/foo.txt'],
+      ['https', '[::1]:8080', '/foo.txt'],
+      ['https', 'localhost', '/'],
+      ['https', 'localhost', '/foo/bar/baz'],
+      ['https', 'localhost', '/foo_bar'],
+      ['https', 'localhost', '/foo//bar'],
+      ['https', 'localhost', '/static/%2e%2e/foo.txt'],
+      ['https', 'localhost', '/static\\..\\foo.txt'],
+      ['https', 'localhost', '/..'],
+      ['https', 'localhost', '/foo/.'],
+      ['https', 'localhost', '/foo/bar/..'],
+      ['https', 'localhost', '/a/b/../../c'],
+      ['https', 'localhost', '/a/../../../b'],
+      ['https', 'localhost', '/a/b/c/../../../'],
+      ['https', 'localhost', '/./foo.txt'],
+      ['https', 'localhost', '/foo/../bar.txt'],
+      ['https', 'localhost', '/a/./b/../c?q=%2E%2E#hash'],
+      ['https', 'localhost', '/foo/%2E/bar/../baz'],
+      ['https', 'localhost', '/hello%20world'],
+      ['https', 'localhost', '/foo%23bar'],
+      ['https', 'localhost', '/foo"bar'],
+      ['https', 'localhost', '/%2e%2E/foo'],
+      ['https', 'localhost', '/caf%C3%A9'],
+      ['https', 'localhost', '/foo%2fbar/..//baz'],
+      ['https', 'localhost', '/foo?q=../bar'],
+      ['https', 'localhost', '/path?q=hello%20world'],
+      ['https', 'localhost', '/file.txt'],
+      ['https', 'localhost', ''],
+      ['http', 'localhost:080', '/foo.txt'],
+      ['http', 'localhost:08080', '/foo.txt'],
+      ['http', 'localhost:80', '/foo.txt'],
+      ['https', 'localhost:80', '/foo.txt'],
+      ['http', 'localhost:443', '/foo.txt'],
+      ['https', 'localhost:443', '/foo.txt'],
+      ['https', 'LOCALHOST', '/foo.txt'],
+      ['https', 'LOCALHOST:80', '/foo.txt'],
+      ['https', 'LOCALHOST:443', '/foo.txt'],
+      ['https', 'LOCALHOST:8080', '/foo.txt'],
+      ['https', 'Localhost:3000', '/foo.txt'],
+    ])('Should successfully normalize `%s://%s%s`', async (scheme, host, path) => {
+      expect(buildUrl(scheme, host, path)).toBe(new URL(path, `${scheme}://${host}`).href)
     })
 
     it('Should throw a RequestError for non-origin-form request-target', async () => {