diff --git a/src/Objects/BlockService.php b/src/Objects/BlockService.php
index d810020..489bafa 100644
--- a/src/Objects/BlockService.php
+++ b/src/Objects/BlockService.php
@@ -2,6 +2,8 @@
 
 namespace ActivityPub\Objects;
 
+use ActivityPub\Entities\ActivityPubObject;
+
 class BlockService
 {
     /**
@@ -23,15 +25,42 @@ class BlockService
      */
     public function getBlockedActorIds( $blockingActorId )
     {
-        $q = array(
+        $blockQuery = array(
             'type' => 'Block',
             'actor' => array(
                 'id' => $blockingActorId,
             ),
         );
-        $blocks = $this->objectsService->query( $q );
+        $blocks = $this->objectsService->query( $blockQuery );
+
+        // TODO this is janky and slow - there's probably a better way
+        $undoQuery = array(
+            'type' => 'Undo',
+            'actor' => array(
+                'id' => $blockingActorId,
+            ),
+            'object' => array(
+                'type' => 'Block',
+            ),
+        );
+        $undos = $this->objectsService->query( $undoQuery );
+        $undoneBlocks = array();
+        foreach ( $undos as $undo ) {
+            if ( $undo->hasField( 'object' ) ) {
+                $undoObject = $undo['object'];
+                if ( is_string( $undoObject ) ) {
+                    $undoneBlocks[$undoObject] = 1;
+                } else if ( $undoObject instanceof ActivityPubObject && $undoObject->hasField( 'id' ) ) {
+                    $undoneBlocks[$undoObject['id']] = 1;
+                }
+            }
+        }
+
         $blockedIds = array();
         foreach ( $blocks as $block ) {
+            if ( array_key_exists( $block['id'], $undoneBlocks ) ) {
+                continue;
+            }
             if ( $block->hasField( 'object' ) ) {
                 $blockedActor = $block['object'];
                 if ( is_string( $blockedActor ) ) {
diff --git a/src/Objects/ObjectsService.php b/src/Objects/ObjectsService.php
index e8176a7..52ef17d 100644
--- a/src/Objects/ObjectsService.php
+++ b/src/Objects/ObjectsService.php
@@ -27,6 +27,11 @@ class ObjectsService
      */
     protected $httpClient;
 
+    /**
+     * @var int
+     */
+    protected $nonce;
+
     public function __construct( EntityManager $entityManager,
                                  DateTimeProvider $dateTimeProvider,
                                  Client $client )
@@ -34,6 +39,7 @@ class ObjectsService
         $this->entityManager = $entityManager;
         $this->dateTimeProvider = $dateTimeProvider;
         $this->httpClient = $client;
+        $this->nonce = 0;
     }
 
     /**
@@ -97,6 +103,12 @@ class ObjectsService
         return $query->getResult();
     }
 
+    protected function getNextNonce()
+    {
+        $this->nonce = $this->nonce + 1;
+        return $this->nonce;
+    }
+
     /**
      * Generates the Doctrine QueryBuilder that represents the query
      *
@@ -104,16 +116,16 @@ class ObjectsService
      *   final expression
      *
      * @param array $queryTerms The query terms from which to generate the expressions
-     * @param int $nonce A nonce value to differentiate field names
      * @return QueryBuilder The expression
      */
-    protected function getObjectQuery( $queryTerms, $nonce = 0 )
+    protected function getObjectQuery( $queryTerms )
     {
+        $nonce = $this->getNextNonce();
         $qb = $this->entityManager->createQueryBuilder();
         $exprs = array();
         foreach ( $queryTerms as $fieldName => $fieldValue ) {
             if ( is_array( $fieldValue ) ) {
-                $subQuery = $this->getObjectQuery( $fieldValue, $nonce + 1 );
+                $subQuery = $this->getObjectQuery( $fieldValue );
                 $exprs[] = $qb->expr()->andX(
                     $qb->expr()->like(
                         "field$nonce.name",
diff --git a/test/Objects/BlockServiceTest.php b/test/Objects/BlockServiceTest.php
index 2ea59fe..3750935 100644
--- a/test/Objects/BlockServiceTest.php
+++ b/test/Objects/BlockServiceTest.php
@@ -156,6 +156,94 @@ class BlockServiceTest extends SQLiteTestCase
                 'blockingActorId' => 'https://example.com/actors/1',
                 'expectedBlockedActorIds' => array( 'https://elsewhere.com/actors/2' ),
             ),
+            array(
+                'id' => 'undoneBlocks',
+                'initialData' => array(
+                    array(
+                        'id' => 'https://example.com/blocks/1',
+                        'type' => 'Block',
+                        'actor' => array(
+                            'id' => 'https://example.com/actors/1',
+                        ),
+                        'object' => array(
+                            'id' => 'https://elsewhere.com/actors/1',
+                        )
+                    ),
+                    array(
+                        'id' => 'https://example.com/blocks/2',
+                        'type' => 'Block',
+                        'actor' => array(
+                            'id' => 'https://example.com/actors/1',
+                        ),
+                        'object' => array(
+                            'id' => 'https://elsewhere.com/actors/2',
+                        )
+                    ),
+                    array(
+                        'id' => 'https://example.com/undos/1',
+                        'type' => 'Undo',
+                        'actor' => array(
+                            'id' => 'https://example.com/actors/1',
+                        ),
+                        'object' => array(
+                            'id' => 'https://example.com/blocks/1',
+                            'type' => 'Block',
+                            'actor' => array(
+                                'id' => 'https://example.com/actors/1',
+                            ),
+                            'object' => array(
+                                'id' => 'https://elsewhere.com/actors/1',
+                            )
+                        )
+                    ),
+                ),
+                'blockingActorId' => 'https://example.com/actors/1',
+                'expectedBlockedActorIds' => array( 'https://elsewhere.com/actors/2' ),
+            ),
+            array(
+                'id' => 'irrelevantUndonBlocks',
+                'initialData' => array(
+                    array(
+                        'id' => 'https://example.com/blocks/1',
+                        'type' => 'Block',
+                        'actor' => array(
+                            'id' => 'https://example.com/actors/1',
+                        ),
+                        'object' => array(
+                            'id' => 'https://elsewhere.com/actors/1',
+                        )
+                    ),
+                    array(
+                        'id' => 'https://example.com/blocks/2',
+                        'type' => 'Block',
+                        'actor' => array(
+                            'id' => 'https://example.com/actors/1',
+                        ),
+                        'object' => array(
+                            'id' => 'https://elsewhere.com/actors/2',
+                        )
+                    ),
+                    array(
+                        'id' => 'https://example.com/undos/1',
+                        'type' => 'Undo',
+                        'actor' => array(
+                            'id' => 'https://example.com/actors/1',
+                        ),
+                        'object' => array(
+                            'id' => 'https://example.com/blocks/3',
+                            'type' => 'Block',
+                            'actor' => array(
+                                'id' => 'https://example.com/actors/1',
+                            ),
+                            'object' => array(
+                                'id' => 'https://elsewhere.com/actors/3',
+                            )
+                        )
+                    ),
+                ),
+                'blockingActorId' => 'https://example.com/actors/1',
+                'expectedBlockedActorIds' => array( 'https://elsewhere.com/actors/1', 'https://elsewhere.com/actors/2' ),
+            )
         );
         foreach ( $testCases as $testCase ) {
             self::setUp();