diff --git a/src/Socialbox/Classes/StandardMethods/AddressBook/AddressBookRevokeSignature.php b/src/Socialbox/Classes/StandardMethods/AddressBook/AddressBookRevokeSignature.php
index 849cf79..8e0426e 100644
--- a/src/Socialbox/Classes/StandardMethods/AddressBook/AddressBookRevokeSignature.php
+++ b/src/Socialbox/Classes/StandardMethods/AddressBook/AddressBookRevokeSignature.php
@@ -14,7 +14,6 @@
     use Socialbox\Objects\ClientRequest;
     use Socialbox\Objects\PeerAddress;
     use Socialbox\Objects\RpcRequest;
-    use Symfony\Component\Uid\Uuid;
 
     class AddressBookRevokeSignature extends Method
     {
@@ -43,20 +42,10 @@
                 throw new MissingRpcArgumentException('signature_uuid');
             }
 
-            try
-            {
-                $signatureUuid = Uuid::fromString($rpcRequest->getParameter('signature_uuid'));
-            }
-            catch(InvalidArgumentException $e)
-            {
-                throw new InvalidRpcArgumentException('signature_uuid', $e);
-            }
-
             try
             {
                 // Check if the contact already exists
-                $peer = $request->getPeer();
-                $contact = ContactManager::getContact($peer, $address);
+                $contact = ContactManager::getContact($request->getPeer(), $address);
             }
             catch (DatabaseOperationException $e)
             {
@@ -70,6 +59,7 @@
 
             try
             {
+                $signatureUuid = (string)$rpcRequest->getParameter('signature_uuid');
                 if(!ContactManager::contactSigningKeyUuidExists($contact, $signatureUuid))
                 {
                     return $rpcRequest->produceResponse(false);
diff --git a/src/Socialbox/Managers/ContactManager.php b/src/Socialbox/Managers/ContactManager.php
index e220249..197fe43 100644
--- a/src/Socialbox/Managers/ContactManager.php
+++ b/src/Socialbox/Managers/ContactManager.php
@@ -7,6 +7,7 @@
     use ncc\ThirdParty\Symfony\Uid\UuidV4;
     use PDO;
     use PDOException;
+    use Socialbox\Classes\Cryptography;
     use Socialbox\Classes\Database;
     use Socialbox\Classes\Validator;
     use Socialbox\Enums\Types\ContactRelationshipType;
@@ -424,6 +425,15 @@
             {
                 $contactUuid = $contactUuid->getUuid();
             }
+            elseif(!Validator::validateUuid($contactUuid))
+            {
+                throw new InvalidArgumentException('The given contact UUID is not a valid UUID V4');
+            }
+
+            if(!Validator::validateUuid($signatureUuid))
+            {
+                throw new InvalidArgumentException('The given signature UUID is not a valid UUID V4');
+            }
 
             try
             {