diff --git a/src/Validator.php b/src/Validator.php
index fc3e199..12e7770 100644
--- a/src/Validator.php
+++ b/src/Validator.php
@@ -87,6 +87,13 @@ public function validateIpAddress(string $ipAddress): bool
         return (bool) filter_var($ipAddress, FILTER_VALIDATE_IP, FILTER_FLAG_NO_PRIV_RANGE);
     }
 
+    public function hasSupportedCountryPrefix(string $vatNumber): bool
+    {
+        $country = substr($vatNumber, 0, 2);
+
+        return isset($this->patterns[$country]);
+    }
+
     /**
      * Validate a VAT number format. This does not check whether the VAT number was really issued.
      *
@@ -105,7 +112,7 @@ public function validateVatNumberFormat(string $vatNumber): bool
         $number = substr($vatNumber, 2);
 
         if (! isset($this->patterns[$country])) {
-            return false;
+            throw new \InvalidArgumentException('The vat country prefix is not supported.');
         }
 
         return preg_match('/^' . $this->patterns[$country] . '$/', $number) > 0;
diff --git a/tests/ValidatorTest.php b/tests/ValidatorTest.php
index 847bc49..b4fb3f3 100644
--- a/tests/ValidatorTest.php
+++ b/tests/ValidatorTest.php
@@ -96,14 +96,6 @@ public function testValidateVatNumberFormat()
             'SI1234567',
             'SK123456789',
 
-            // valid number but with prefix
-            'invalid_prefix_GB999999973',
-            'invalid_prefix_IE1234567X',
-            'invalid_prefix_ESB1234567C',
-            'invalid_prefix_BE0123456789',
-            'invalid_prefix_MT12345678',
-            'invalid_prefix_LT123456789',
-
             // valid number but with suffix
             'IE1234567X_invalid_suffix',
             'ESB1234567C_invalid_suffix',