diff --git a/src/wp-includes/functions.php b/src/wp-includes/functions.php
index af88d3b06d..9a6938ed64 100644
--- a/src/wp-includes/functions.php
+++ b/src/wp-includes/functions.php
@@ -6273,7 +6273,7 @@ function validate_file( $file, $allowed_files = array() ) {
  *
  * @since 2.6.0
  *
- * @param string|bool $force Optional. Whether to force SSL in admin screens. Default null.
+ * @param string|bool|null $force Optional. Whether to force SSL in admin screens. Default null.
  * @return bool True if forced, false if not forced.
  */
 function force_ssl_admin( $force = null ) {
@@ -6281,7 +6281,7 @@ function force_ssl_admin( $force = null ) {
 
 	if ( ! is_null( $force ) ) {
 		$old_forced = $forced;
-		$forced     = $force;
+		$forced     = (bool) $force;
 		return $old_forced;
 	}
 
diff --git a/tests/phpunit/tests/functions/forceSslAdmin.php b/tests/phpunit/tests/functions/forceSslAdmin.php
new file mode 100644
index 0000000000..a700310443
--- /dev/null
+++ b/tests/phpunit/tests/functions/forceSslAdmin.php
@@ -0,0 +1,55 @@
+<?php
+/**
+ * Test cases for the `force_ssl_admin()` function.
+ *
+ * @package WordPress\UnitTests
+ *
+ * @since 6.8.0
+ *
+ * @group functions
+ *
+ * @covers ::force_ssl_admin
+ */
+class Tests_Functions_ForceSslAdmin extends WP_UnitTestCase {
+
+	public function set_up(): void {
+		parent::set_up();
+		// Reset the static variable before each test
+		force_ssl_admin( false );
+	}
+
+	/**
+	 * Data provider for testing force_ssl_admin.
+	 *
+	 * Provides various inputs and expected outcomes for the function.
+	 *
+	 * @return array[]
+	 */
+	public function data_should_return_expected_value_when_various_inputs_are_passed() {
+		return array(
+			'default'                     => array( null, false, false ),
+			'first_call_true'             => array( true, false, true ),
+			'first_call_false'            => array( false, false, false ),
+			'first_call_non_empty_string' => array( 'some string', false, true ),
+			'empty_string'                => array( '', false, false ),
+			'first_call_integer_1'        => array( 1, false, true ),
+			'integer_0'                   => array( 0, false, false ),
+		);
+	}
+
+	/**
+	 * Tests that force_ssl_admin returns expected values based on various inputs.
+	 *
+	 * @dataProvider data_should_return_expected_value_when_various_inputs_are_passed
+	 *
+	 * @param mixed $input                   The input value to test.
+	 * @param bool $expected_first_call      The expected result for the first call.
+	 * @param bool $expected_subsequent_call The expected result for subsequent calls.
+	 */
+	public function test_should_return_expected_value_when_various_inputs_are_passed( $input, $expected_first_call, $expected_subsequent_call ) {
+		$this->assertSame( $expected_first_call, force_ssl_admin( $input ), 'First call did not return expected value' );
+
+		// Call again to check subsequent behavior
+		$this->assertSame( $expected_subsequent_call, force_ssl_admin( $input ), 'Subsequent call did not return expected value' );
+	}
+}