diff --git a/src/wp-includes/canonical.php b/src/wp-includes/canonical.php
index 58723ebc0d8a4..00db00c3c8bcd 100644
--- a/src/wp-includes/canonical.php
+++ b/src/wp-includes/canonical.php
@@ -600,6 +600,10 @@ function redirect_canonical( $requested_url = null, $do_redirect = true ) {
 	// www.example.com vs. example.com
 	$user_home = parse_url( home_url() );
 
+	if ( ! empty( $user_home['scheme'] ) ) {
+		$redirect['scheme'] = $user_home['scheme'];
+	}
+
 	if ( ! empty( $user_home['host'] ) ) {
 		$redirect['host'] = $user_home['host'];
 	}
@@ -717,13 +721,24 @@ function redirect_canonical( $requested_url = null, $do_redirect = true ) {
 	$original_host_low = strtolower( $original['host'] );
 	$redirect_host_low = strtolower( $redirect['host'] );
 
+	$original_port = isset( $original['port'] ) ? strtolower( $original['port'] ) : '80';
+	$redirect_port = isset( $redirect['port'] ) ? strtolower( $redirect['port'] ) : '80';
+
 	/*
-	 * Ignore differences in host capitalization, as this can lead to infinite redirects.
-	 * Only redirect no-www <=> yes-www.
+	 * Preserve original host casing if the hostnames are identical (ignoring case),
+	 * or differ in a way that is not just a www <=> non-www variation,
+	 * and the port is the same.
+	 *
+	 * This prevents unnecessary redirects and avoids redirect loops due to host casing,
+	 * but still allows canonical redirects between www and non-www variants.
 	 */
-	if ( $original_host_low === $redirect_host_low
-		|| ( 'www.' . $original_host_low !== $redirect_host_low
-			&& 'www.' . $redirect_host_low !== $original_host_low )
+	if (
+		$original_host_low === $redirect_host_low
+		|| (
+			'www.' . $original_host_low !== $redirect_host_low
+			&& 'www.' . $redirect_host_low !== $original_host_low
+			&& $original_port === $redirect_port
+		)
 	) {
 		$redirect['host'] = $original['host'];
 	}
diff --git a/tests/phpunit/tests/canonical.php b/tests/phpunit/tests/canonical.php
index 886b09312910e..140d8fbcf26b5 100644
--- a/tests/phpunit/tests/canonical.php
+++ b/tests/phpunit/tests/canonical.php
@@ -545,4 +545,92 @@ public function data_canonical_attachment_page_redirect_with_option_disabled() {
 			),
 		);
 	}
+
+	/**
+	 * Test domain and port redirections.
+	 *
+	 * @ticket 33821
+	 * @dataProvider data_domain_and_port_redirections
+	 *
+	 * @covers ::redirect_canonical
+	 *
+	 * @param string $home_url      The home URL to set.
+	 * @param string $site_url      The site URL to set.
+	 * @param string $request_url   The URL to test redirection for.
+	 * @param string $expected_url  The expected redirect URL, or null if no redirect.
+	 * @param string $failure_msg   The message to display on test failure.
+	 */
+	public function test_domain_and_port_redirections( $home_url, $site_url, $request_url, $expected_url, $failure_msg ) {
+		update_option( 'home', $home_url );
+		update_option( 'siteurl', $site_url );
+
+		$redirect = redirect_canonical( $request_url, false );
+
+		$this->assertSame( $expected_url, $redirect, $failure_msg );
+	}
+
+	/**
+	 * Data provider for test_domain_and_port_redirections().
+	 *
+	 * @return array[] {
+	 *     @type string $home_url      The home URL to set.
+	 *     @type string $site_url      The site URL to set.
+	 *     @type string $request_url   The URL to test redirection for.
+	 *     @type string $expected_url  The expected redirect URL, or null if no redirect.
+	 *     @type string $failure_msg   The message to display on test failure.
+	 * }
+	 */
+	public function data_domain_and_port_redirections() {
+		return array(
+			'non-standard localhost port to canonical domain' => array(
+				'home_url'     => 'http://example.com',
+				'site_url'     => 'http://example.com',
+				'request_url'  => 'http://localhost:10020/',
+				'expected_url' => 'http://example.com/',
+				'failure_msg'  => 'Failed to redirect non-standard localhost port to canonical domain',
+			),
+			'non-standard localhost port to canonical domain with SSL' => array(
+				'home_url'     => 'https://example.com',
+				'site_url'     => 'https://example.com',
+				'request_url'  => 'http://localhost:10020/',
+				'expected_url' => 'https://example.com/',
+				'failure_msg'  => 'Failed to redirect non-standard localhost port to canonical domain with SSL',
+			),
+			'different host casing do not redirect' => array(
+				'home_url'     => 'http://example.com',
+				'site_url'     => 'http://example.com',
+				'request_url'  => 'http://Example.com/',
+				'expected_url' => null,
+				'failure_msg'  => 'Should not redirect when only host casing differs',
+			),
+			'different host casing with port redirect without host change' => array(
+				'home_url'     => 'http://example.com:8080',
+				'site_url'     => 'http://example.com:8080',
+				'request_url'  => 'http://Example.com:10200/',
+				'expected_url' => 'http://Example.com:8080/',
+				'failure_msg'  => 'Failed to redirect to correct port while preserving host casing',
+			),
+			'www to non-www'                        => array(
+				'home_url'     => 'http://example.com',
+				'site_url'     => 'http://example.com',
+				'request_url'  => 'http://www.example.com/',
+				'expected_url' => 'http://example.com/',
+				'failure_msg'  => 'Failed to redirect www to non-www domain',
+			),
+			'non-www to www'                        => array(
+				'home_url'     => 'http://www.example.com',
+				'site_url'     => 'http://www.example.com',
+				'request_url'  => 'http://example.com/',
+				'expected_url' => 'http://www.example.com/',
+				'failure_msg'  => 'Failed to redirect non-www to www domain',
+			),
+			'port for same host'                    => array(
+				'home_url'     => 'http://example.com:8080',
+				'site_url'     => 'http://example.com:8080',
+				'request_url'  => 'http://example.com:10200/',
+				'expected_url' => 'http://example.com:8080/',
+				'failure_msg'  => 'Failed to redirect to correct port for same host',
+			),
+		);
+	}
 }