diff --git a/lib/experimental/fonts/font-library/class-wp-font-family.php b/lib/experimental/fonts/font-library/class-wp-font-family.php
index a4f55d8c0cece7..309b1c8b7902b5 100644
--- a/lib/experimental/fonts/font-library/class-wp-font-family.php
+++ b/lib/experimental/fonts/font-library/class-wp-font-family.php
@@ -300,12 +300,17 @@ private function sanitize() {
 			'version'  => '2',
 			'settings' => array(
 				'typography' => array(
-					'fontFamilies' => array( $this->data ),
+					'fontFamilies' => array(
+						'custom' => array(
+							$this->data,
+						),
+					),
 				),
 			),
 		);
 		// Creates a new WP_Theme_JSON object with the new fonts to
 		// leverage sanitization and validation.
+		$fonts_json     = WP_Theme_JSON_Gutenberg::remove_insecure_properties( $fonts_json );
 		$theme_json     = new WP_Theme_JSON_Gutenberg( $fonts_json );
 		$theme_data     = $theme_json->get_data();
 		$sanitized_font = ! empty( $theme_data['settings']['typography']['fontFamilies'] )
diff --git a/phpunit/class-wp-theme-json-test.php b/phpunit/class-wp-theme-json-test.php
index 6ccbe2fb1d03ba..e0c11766eaaae3 100644
--- a/phpunit/class-wp-theme-json-test.php
+++ b/phpunit/class-wp-theme-json-test.php
@@ -896,6 +896,52 @@ public function test_remove_invalid_element_pseudo_selectors() {
 		$this->assertEqualSetsWithIndex( $expected, $actual );
 	}
 
+	public function test_remove_invalid_font_family_settings() {
+		$actual = WP_Theme_JSON_Gutenberg::remove_insecure_properties(
+			array(
+				'version'  => WP_Theme_JSON_Gutenberg::LATEST_SCHEMA,
+				'settings' => array(
+					'typography' => array(
+						'fontFamilies' => array(
+							'custom' => array(
+								array(
+									'name'       => 'Open Sans',
+									'slug'       => 'open-sans',
+									'fontFamily' => '"Open Sans", sans-serif</style><script>alert("xss")</script>',
+								),
+								array(
+									'name'       => 'Arial',
+									'slug'       => 'arial',
+									'fontFamily' => 'Arial, serif',
+								),
+							),
+						),
+					),
+				),
+			),
+			true
+		);
+
+		$expected = array(
+			'version'  => WP_Theme_JSON_Gutenberg::LATEST_SCHEMA,
+			'settings' => array(
+				'typography' => array(
+					'fontFamilies' => array(
+						'custom' => array(
+							array(
+								'name'       => 'Arial',
+								'slug'       => 'arial',
+								'fontFamily' => 'Arial, serif',
+							),
+						),
+					),
+				),
+			),
+		);
+
+		$this->assertEqualSetsWithIndex( $expected, $actual );
+	}
+
 	public function test_get_element_class_name_button() {
 		$expected = 'wp-element-button';
 		$actual   = WP_Theme_JSON_Gutenberg::get_element_class_name( 'button' );