diff --git a/src/DgiiRncValidator.php b/src/DgiiRncValidator.php
index 4ad0c2b..40c30c8 100755
--- a/src/DgiiRncValidator.php
+++ b/src/DgiiRncValidator.php
@@ -16,6 +16,11 @@ class DgiiRncValidator
     public static function validateRNC(string $string): bool
     {
         $cleanedId = Utils::getNumbers($string);
+
+		if (!$cleanedId) {
+			return false;
+		}
+
         preg_match('/^(\d{9}|\d{11})$/', $cleanedId, $matches);
 
         return (bool) count($matches);
diff --git a/tests/DgiiRncValidatorTest.php b/tests/DgiiRncValidatorTest.php
index b12dd40..203fee6 100644
--- a/tests/DgiiRncValidatorTest.php
+++ b/tests/DgiiRncValidatorTest.php
@@ -28,3 +28,12 @@
         ->and(DgiiRncValidator::check('123456789'))
         ->toBeFalse();
 });
+
+test('check if the given string without numbers is a valid RNC', function () {
+	$id = 'abc cdd';
+	expect(DgiiRncValidator::validateRNC($id))->toBeFalse();
+	$id = ' ';
+	expect(DgiiRncValidator::validateRNC($id))->toBeFalse();
+	$id = '';
+	expect(DgiiRncValidator::validateRNC($id))->toBeFalse();
+});