diff --git a/src/Grant/AuthCodeGrant.php b/src/Grant/AuthCodeGrant.php
index 6f2b6ff8..6a342228 100644
--- a/src/Grant/AuthCodeGrant.php
+++ b/src/Grant/AuthCodeGrant.php
@@ -249,9 +249,9 @@ class AuthCodeGrant extends AbstractAuthorizeGrant
 
         $scopes = $this->validateScopes(
             $this->getQueryStringParameter('scope', $request, $this->defaultScope),
-            is_array($client->getRedirectUri())
+            $redirectUri ?: (is_array($client->getRedirectUri())
                 ? $client->getRedirectUri()[0]
-                : $client->getRedirectUri()
+                : $client->getRedirectUri())
         );
 
         $stateParameter = $this->getQueryStringParameter('state', $request);
diff --git a/src/Grant/ImplicitGrant.php b/src/Grant/ImplicitGrant.php
index f3c9e694..a10ac642 100644
--- a/src/Grant/ImplicitGrant.php
+++ b/src/Grant/ImplicitGrant.php
@@ -158,9 +158,9 @@ class ImplicitGrant extends AbstractAuthorizeGrant
 
         $scopes = $this->validateScopes(
             $this->getQueryStringParameter('scope', $request, $this->defaultScope),
-            is_array($client->getRedirectUri())
+            $redirectUri ?: (is_array($client->getRedirectUri())
                 ? $client->getRedirectUri()[0]
-                : $client->getRedirectUri()
+                : $client->getRedirectUri())
         );
 
         // Finalize the requested scopes