diff --git a/cloudinary-image-management-and-manipulation-in-the-cloud-cdn/php/class-settings-page.php b/cloudinary-image-management-and-manipulation-in-the-cloud-cdn/php/class-settings-page.php
index 42be6ab5d..237c61557 100644
--- a/cloudinary-image-management-and-manipulation-in-the-cloud-cdn/php/class-settings-page.php
+++ b/cloudinary-image-management-and-manipulation-in-the-cloud-cdn/php/class-settings-page.php
@@ -412,7 +412,18 @@ public function sanitize( $setting, $fields ) {
 				}
 			} else {
 				if ( is_array( $field ) ) {
-					array_walk_recursive( $field, 'sanitize_text_field' );
+					array_walk_recursive(
+						$field,
+						static function( $field_value ) {
+							// WP 4.9 compatibility, as _sanitize_text_fields() didn't have this check yet, and this prevents an error.
+							// @see https://github.com/WordPress/wordpress-develop/blob/b30baca3ca2feb7f44b3615262ca55fcd87ae232/src/wp-includes/formatting.php#L5307
+							if ( is_object( $field_value ) || is_array( $field_value ) ) {
+								return '';
+							}
+
+							return sanitize_text_field( $field_value );
+						}
+					);
 				} else {
 					$setting[ $slug ] = sanitize_text_field( $field );
 				}