diff --git a/utils/vanitygen.php b/utils/vanitygen.php
index fd3d5a28..49291f0f 100644
--- a/utils/vanitygen.php
+++ b/utils/vanitygen.php
@@ -1,7 +1,7 @@
 <?php
 
 const VANITYGEN_NAME = 'PHPCoin Vanity Address Generator';
-const VANITYGEN_VERSION = '0.0.1';
+const VANITYGEN_VERSION = '0.0.2';
 const VANITYGEN_USAGE = 'Usage: php vanitygen.php prefix [-c] [-d]' . PHP_EOL .
     '  prefix     Prefix for the PHPCoin address (e.g., "Php")' . PHP_EOL .
     '  -c         Case sensitive matching' . PHP_EOL .
@@ -15,10 +15,72 @@
 
 setupOrExit();
 
-generateVanityAddress(getOptionsOrExit($argv));
+$options = getOptionsOrExit($argv);
+
+// First, validate the original, user-provided prefix.
+validatePrefix($options['prefix'], $options['case_sensitive']);
+
+// If validation passes, normalize the prefix for the generator.
+$options['prefix'] = normalizePrefix($options['prefix']);
+
+// Finally, generate the address with the normalized prefix.
+generateVanityAddress($options);
 
 print PHP_EOL . 'Exiting ' . VANITYGEN_NAME . PHP_EOL;
 
+/**
+ * Normalizes a prefix to ensure it starts with a capital 'P'.
+ *
+ * @param string $prefix The user-provided prefix.
+ * @return string The normalized prefix.
+ */
+function normalizePrefix(string $prefix): string
+{
+    // If the prefix starts with 'p' (case-insensitively), replace the first char with 'P'.
+    if (strtolower(substr($prefix, 0, 1)) === 'p') {
+        return 'P' . substr($prefix, 1);
+    }
+    // Otherwise, prepend 'P'.
+    return 'P' . $prefix;
+}
+
+/**
+ * Validates the provided prefix against the list of mathematically possible second characters.
+ *
+ * Exits with an error message if the prefix is invalid.
+ *
+ * @param string $prefix The prefix to validate.
+ * @param bool $caseSensitive Whether the check should be case sensitive.
+ */
+function validatePrefix(string $prefix, bool $caseSensitive): void
+{
+    // It is assumed the prefix has been normalized before being passed to this function.
+    if (strlen($prefix) < 2) {
+        return; // Not long enough for a 2-char check.
+    }
+
+    $prefixToCheck = substr($prefix, 0, 2);
+
+    $validPrefixes = [
+        'PX', 'PY', 'PZ', 'Pa', 'Pb', 'Pc', 'Pd', 'Pe', 'Pf', 'Pg', 'Ph', 'Pi', 'Pj', 'Pk', 'Pm', 'Pn', 'Po', 'Pp', 'Pq', 'Pr', 'Ps', 'Pt', 'Pu', 'Pv', 'Pw'
+    ];
+
+    $isValid = false;
+    if ($caseSensitive) {
+        $isValid = in_array($prefixToCheck, $validPrefixes, true);
+    } else {
+        // For case-insensitive, we compare the lowercase versions.
+        $lowerValidPrefixes = array_map('strtolower', $validPrefixes);
+        $isValid = in_array(strtolower($prefixToCheck), $lowerValidPrefixes);
+    }
+
+    if (!$isValid) {
+        sort($validPrefixes);
+        $validPrefixesList = implode(', ', $validPrefixes);
+        exit('ERROR: Impossible prefix.' . PHP_EOL . 'Valid prefixes start with: ' . $validPrefixesList . PHP_EOL);
+    }
+}
+
 /**
  * Generates a vanity PHPCoin address based on the provided options.
  *
@@ -30,15 +92,6 @@
 function generateVanityAddress(array $options): array
 {
     $prefix = $options['prefix'];
-    // All PHPCoin addresses start with uppercase 'P'
-    if (! str_starts_with($prefix, 'p') && ! str_starts_with($prefix, 'P')) {
-        $prefix = 'P' . $prefix;
-    }
-    // Force starting with uppercase 'P'
-    if (str_starts_with($prefix, 'p')) {
-        $prefix = 'P' . substr($prefix, 1);
-    }
-
     $caseSensitive = $options['case_sensitive'];
 
     print 'Prefix: ' . $prefix . PHP_EOL;
@@ -132,7 +185,7 @@ function getOptionsOrExit(array $argv): array
 
     return [
         'prefix' => $arguments[0],
-        'case_sensitive' => isset($options['c']) ? true : false,
+        'case_sensitive' => isset($options['c'])
     ];
 }
 
diff --git a/vendor/composer/LICENSE b/vendor/composer/LICENSE
index f27399a0..da27360b 100644
--- a/vendor/composer/LICENSE
+++ b/vendor/composer/LICENSE
@@ -18,4 +18,3 @@ AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 THE SOFTWARE.
-