diff --git a/src/wp-includes/formatting.php b/src/wp-includes/formatting.php
index c524b06928..576b3c657a 100644
--- a/src/wp-includes/formatting.php
+++ b/src/wp-includes/formatting.php
@@ -2137,8 +2137,15 @@ function sanitize_user( $username, $strict = false ) {
  */
 function sanitize_key( $key ) {
 	$raw_key = $key;
-	$key     = strtolower( $key );
-	$key     = preg_replace( '/[^a-z0-9_\-]/', '', $key );
+
+	if ( ! is_string( $key ) ) {
+		$key = '';
+	}
+
+	if ( '' !== $key ) {
+		$key = strtolower( $key );
+		$key = preg_replace( '/[^a-z0-9_\-]/', '', $key );
+	}
 
 	/**
 	 * Filters a sanitized key string.
diff --git a/tests/phpunit/tests/formatting/sanitizeKey.php b/tests/phpunit/tests/formatting/sanitizeKey.php
new file mode 100644
index 0000000000..7dea43e004
--- /dev/null
+++ b/tests/phpunit/tests/formatting/sanitizeKey.php
@@ -0,0 +1,90 @@
+<?php
+
+/**
+ * @group formatting
+ * @covers ::sanitize_key
+ */
+class Tests_Formatting_SanitizeKey extends WP_UnitTestCase {
+
+	/**
+	 * @ticket 54160
+	 * @dataProvider data_sanitize_key
+	 *
+	 * @param mixed $key       The key to sanitize.
+	 * @param mixed $expected  The expected value.
+	 */
+	public function test_sanitize_key( $key, $expected ) {
+		$this->assertSame( $expected, sanitize_key( $key ) );
+	}
+
+	public function data_sanitize_key() {
+		return array(
+			'an empty string key'            => array(
+				'key'      => '',
+				'expected' => '',
+			),
+			'a null key'                     => array(
+				'key'      => null,
+				'expected' => '',
+			),
+			'an int 0 key'                   => array(
+				'key'      => 0,
+				'expected' => '',
+			),
+			'a true key'                     => array(
+				'key'      => true,
+				'expected' => '',
+			),
+			'an array key'                   => array(
+				'key'      => array( 'Howdy, admin!' ),
+				'expected' => '',
+			),
+			'a lowercase key with commas'    => array(
+				'key'      => 'howdy,admin',
+				'expected' => 'howdyadmin',
+			),
+			'a lowercase key with commas'    => array(
+				'key'      => 'HOWDY,ADMIN',
+				'expected' => 'howdyadmin',
+			),
+			'a mixed case key with commas'   => array(
+				'key'      => 'HoWdY,aDmIn',
+				'expected' => 'howdyadmin',
+			),
+			'a key with dashes'              => array(
+				'key'      => 'howdy-admin',
+				'expected' => 'howdy-admin',
+			),
+			'a key with spaces'              => array(
+				'key'      => 'howdy admin',
+				'expected' => 'howdyadmin',
+			),
+			'a key with a HTML entity'       => array(
+				'key'      => 'howdy&nbsp;admin',
+				'expected' => 'howdynbspadmin',
+			),
+			'a key with a unicode character' => array(
+				'key'      => 'howdy' . chr( 140 ) . 'admin',
+				'expected' => 'howdyadmin',
+			),
+		);
+	}
+
+	/**
+	 * @ticket 54160
+	 *
+	 * @covers WP_Hook::sanitize_key
+	 */
+	public function test_filter_sanitize_key() {
+		$key = 'Howdy, admin!';
+
+		add_filter(
+			'sanitize_key',
+			static function( $key ) {
+				return 'Howdy, admin!';
+			}
+		);
+
+		$this->assertSame( $key, sanitize_key( $key ) );
+	}
+}