diff --git a/src/wp-includes/compat.php b/src/wp-includes/compat.php
index e64af9ab38..02eb4eb6dc 100644
--- a/src/wp-includes/compat.php
+++ b/src/wp-includes/compat.php
@@ -435,6 +435,49 @@ if ( ! function_exists( 'str_contains' ) ) {
 	}
 }
 
+if ( ! function_exists( 'str_starts_with' ) ) {
+	/**
+	 * Polyfill for `str_starts_with()` function added in PHP 8.0.
+	 *
+	 * Performs a case-sensitive check indicating if
+	 * the haystack begins with needle.
+	 *
+	 * @since 5.9.0
+	 *
+	 * @param string $haystack The string to search in.
+	 * @param string $needle   The substring to search for in the `$haystack`.
+	 * @return bool True if `$haystack` starts with `$needle`, otherwise false.
+	 */
+	function str_starts_with( $haystack, $needle ) {
+		if ( '' === $needle ) {
+			return true;
+		}
+		return 0 === strpos( $haystack, $needle );
+	}
+}
+
+if ( ! function_exists( 'str_ends_with' ) ) {
+	/**
+	 * Polyfill for `str_ends_with()` function added in PHP 8.0.
+	 *
+	 * Performs a case-sensitive check indicating if
+	 * the haystack ends with needle.
+	 *
+	 * @since 5.9.0
+	 *
+	 * @param string $haystack The string to search in.
+	 * @param string $needle   The substring to search for in the `$haystack`.
+	 * @return bool True if `$haystack` ends with `$needle`, otherwise false.
+	 */
+	function str_ends_with( $haystack, $needle ) {
+		if ( '' === $haystack && '' !== $needle ) {
+			return false;
+		}
+		$len = strlen( $needle );
+		return 0 === substr_compare( $haystack, $needle, -$len, $len );
+	}
+}
+
 // IMAGETYPE_WEBP constant is only defined in PHP 7.1 or later.
 if ( ! defined( 'IMAGETYPE_WEBP' ) ) {
 	define( 'IMAGETYPE_WEBP', 18 );
diff --git a/tests/phpunit/tests/compat/strEndsWith.php b/tests/phpunit/tests/compat/strEndsWith.php
new file mode 100644
index 0000000000..75522d6f49
--- /dev/null
+++ b/tests/phpunit/tests/compat/strEndsWith.php
@@ -0,0 +1,115 @@
+<?php
+
+/**
+ * @group compat
+ *
+ * @covers ::str_ends_with
+ */
+class Tests_Compat_StrEndsWith extends WP_UnitTestCase {
+
+	/**
+	 * Test that str_ends_with() is always available (either from PHP or WP).
+	 *
+	 * @ticket 54377
+	 */
+	public function test_str_ends_with_availability() {
+		$this->assertTrue( function_exists( 'str_ends_with' ) );
+	}
+
+	/**
+	 * @dataProvider data_str_ends_with
+	 *
+	 * @ticket 54377
+	 *
+	 * @param bool   $expected Whether or not `$haystack` is expected to end with `$needle`.
+	 * @param string $haystack The string to search in.
+	 * @param string $needle   The substring to search for at the end of `$haystack`.
+	 */
+	public function test_str_ends_with( $expected, $haystack, $needle ) {
+		if ( ! function_exists( 'str_ends_with' ) ) {
+			$this->markTestSkipped( 'str_ends_with() is not available.' );
+		} else {
+			$this->assertSame(
+				$expected,
+				str_ends_with( $haystack, $needle )
+			);
+		}
+
+	}
+
+	/**
+	 * Data provider.
+	 *
+	 * @return array[]
+	 */
+	public function data_str_ends_with() {
+		return array(
+			'empty needle'              => array(
+				'expected' => true,
+				'haystack' => 'This is a test',
+				'needle'   => '',
+			),
+			'empty haystack and needle' => array(
+				'expected' => true,
+				'haystack' => '',
+				'needle'   => '',
+			),
+			'empty haystack'            => array(
+				'expected' => false,
+				'haystack' => '',
+				'needle'   => 'test',
+			),
+			'lowercase'                 => array(
+				'expected' => true,
+				'haystack' => 'This is a test',
+				'needle'   => 'test',
+			),
+			'uppercase'                 => array(
+				'expected' => true,
+				'haystack' => 'This is a TEST',
+				'needle'   => 'TEST',
+			),
+			'first letter uppercase'    => array(
+				'expected' => true,
+				'haystack' => 'This is a Test',
+				'needle'   => 'Test',
+			),
+			'camelCase'                 => array(
+				'expected' => true,
+				'haystack' => 'This is a camelCase',
+				'needle'   => 'camelCase',
+			),
+			'null'                      => array(
+				'expected' => true,
+				'haystack' => 'This is a null \x00test',
+				'needle'   => '\x00test',
+			),
+			'trademark'                 => array(
+				'expected' => true,
+				'haystack' => 'This is a trademark\x2122',
+				'needle'   => 'trademark\x2122',
+			),
+			'not camelCase'             => array(
+				'expected' => false,
+				'haystack' => 'This is a cammelcase',
+				'needle'   => 'cammelCase',
+			),
+			'missing'                   => array(
+				'expected' => false,
+				'haystack' => 'This is a cammelcase',
+				'needle'   => 'cammelCase',
+			),
+			'not end'                   => array(
+				'expected' => false,
+				'haystack' => 'This is a test extra',
+				'needle'   => 'test',
+			),
+			'extra space'               => array(
+				'expected' => false,
+				'haystack' => 'This is a test ',
+				'needle'   => 'test',
+			),
+
+		);
+	}
+}
diff --git a/tests/phpunit/tests/compat/strStartsWith.php b/tests/phpunit/tests/compat/strStartsWith.php
new file mode 100644
index 0000000000..9e12ced33b
--- /dev/null
+++ b/tests/phpunit/tests/compat/strStartsWith.php
@@ -0,0 +1,119 @@
+<?php
+
+/**
+ * @group compat
+ *
+ * @covers ::str_starts_with
+ */
+class Tests_Compat_StrStartsWith extends WP_UnitTestCase {
+
+	/**
+	 * Test that str_starts_with() is always available (either from PHP or WP).
+	 *
+	 * @ticket 54377
+	 */
+	public function test_str_starts_with_availability() {
+		$this->assertTrue( function_exists( 'str_starts_with' ) );
+	}
+
+	/**
+	 * @dataProvider data_str_starts_with
+	 *
+	 * @ticket 54377
+	 *
+	 * @param bool   $expected Whether or not `$haystack` is expected to start with `$needle`.
+	 * @param string $haystack The string to search in.
+	 * @param string $needle   The substring to search for at the start of `$haystack`.
+	 */
+	public function test_str_starts_with( $expected, $haystack, $needle ) {
+		if ( ! function_exists( 'str_starts_with' ) ) {
+			$this->markTestSkipped( 'str_starts_with() is not available.' );
+		} else {
+			$this->assertSame(
+				$expected,
+				str_starts_with( $haystack, $needle )
+			);
+		}
+
+	}
+
+	/**
+	 * Data provider.
+	 *
+	 * @return array[]
+	 */
+	public function data_str_starts_with() {
+		return array(
+			'empty needle'              => array(
+				'expected' => true,
+				'haystack' => 'This is a test',
+				'needle'   => '',
+			),
+			'empty haystack and needle' => array(
+				'expected' => true,
+				'haystack' => '',
+				'needle'   => '',
+			),
+			'empty haystack'            => array(
+				'expected' => false,
+				'haystack' => '',
+				'needle'   => 'test',
+			),
+			'lowercase'                 => array(
+				'expected' => true,
+				'haystack' => 'this is a test',
+				'needle'   => 'this',
+			),
+			'uppercase'                 => array(
+				'expected' => true,
+				'haystack' => 'THIS is a TEST',
+				'needle'   => 'THIS',
+			),
+			'first letter uppercase'    => array(
+				'expected' => true,
+				'haystack' => 'This is a Test',
+				'needle'   => 'This',
+			),
+			'case mismatch'             => array(
+				'expected' => false,
+				'haystack' => 'This is a test',
+				'needle'   => 'this',
+			),
+			'camelCase'                 => array(
+				'expected' => true,
+				'haystack' => 'camelCase is the start',
+				'needle'   => 'camelCase',
+			),
+			'null'                      => array(
+				'expected' => true,
+				'haystack' => 'This\x00is a null test ',
+				'needle'   => 'This\x00is',
+			),
+			'trademark'                 => array(
+				'expected' => true,
+				'haystack' => 'trademark\x2122 is a null test ',
+				'needle'   => 'trademark\x2122',
+			),
+			'not camelCase'             => array(
+				'expected' => false,
+				'haystack' => ' cammelcase is the start',
+				'needle'   => 'cammelCase',
+			),
+			'missing'                   => array(
+				'expected' => false,
+				'haystack' => 'This is a test',
+				'needle'   => 'camelCase',
+			),
+			'not start'                 => array(
+				'expected' => false,
+				'haystack' => 'This is a test extra',
+				'needle'   => 'test',
+			),
+			'extra_space'               => array(
+				'expected' => false,
+				'haystack' => ' This is a test',
+				'needle'   => 'This',
+			),
+		);
+	}
+}