diff --git a/src/OAuth2/Grant/ClientCredentials.php b/src/OAuth2/Grant/ClientCredentials.php
index 9b90f55b..19103e3e 100644
--- a/src/OAuth2/Grant/ClientCredentials.php
+++ b/src/OAuth2/Grant/ClientCredentials.php
@@ -106,13 +106,19 @@ class ClientCredentials implements GrantTypeInterface {
             if ($scopes[$i] === '') unset($scopes[$i]); // Remove any junk scopes
         }
 
+        if ($this->authServer->scopeParamRequired() === true && count($scopes) === 0) {
+            throw new Exception\ClientException(sprintf($this->authServer->getExceptionMessage('invalid_request'), 'scope'), 0);
+        } elseif (count($scopes) === 0 && $this->authServer->getDefaultScope()) {
+            $scopes = array($this->authServer->getDefaultScope());
+        }
+
         $authParams['scopes'] = array();
 
         foreach ($scopes as $scope) {
             $scopeDetails = $this->authServer->getStorage('scope')->getScope($scope);
 
             if ($scopeDetails === false) {
-                throw new Exception\ClientException(sprintf(self::$exceptionMessages['invalid_scope'], $scope), 4);
+                throw new Exception\ClientException(sprintf($this->authServer->getExceptionMessage('invalid_scope'), $scope), 4);
             }
 
             $authParams['scopes'][] = $scopeDetails;