diff --git a/src/InMemoryDocumentStore.php b/src/InMemoryDocumentStore.php
index d7e2c25..361eb07 100644
--- a/src/InMemoryDocumentStore.php
+++ b/src/InMemoryDocumentStore.php
@@ -379,9 +379,15 @@ private function assertUniqueFieldConstraint(string $collectionName, string $doc
 
         $check = new EqFilter($index->field(), $value);
 
-        $existingDocs = $this->filterDocs($collectionName, $check);
+        foreach ($this->inMemoryConnection['documents'][$collectionName] as $existingDocId => $existingDoc) {
+            if (!$check->match($existingDoc, (string)$existingDocId)) {
+                continue;
+            }
+
+            if ((string)$existingDocId === $docId) {
+                continue;
+            }
 
-        foreach ($existingDocs as $existingDoc) {
             throw new RuntimeException(
                 $errMsg ?? "Unique constraint violation. Cannot insert or update document with id $docId, because a document with same value for field: {$index->field()} exists already!"
             );
@@ -434,9 +440,15 @@ private function assertMultiFieldUniqueConstraint(string $collectionName, string
             $checkList = $checkList[0];
         }
 
-        $existingDocs = $this->filterDocs($collectionName, $checkList);
+        foreach ($this->inMemoryConnection['documents'][$collectionName] as $existingDocId => $existingDoc) {
+            if (!$checkList->match($existingDoc, (string)$existingDocId)) {
+                continue;
+            }
+
+            if ((string)$existingDocId === $docId) {
+                continue;
+            }
 
-        foreach ($existingDocs as $existingDoc) {
             $fieldNamesStr = implode(", ", $fieldNames);
             throw new RuntimeException(
                 $errMsg ?? "Unique constraint violation. Cannot insert or update document with id $docId, because a document with same values for fields: {$fieldNamesStr} exists already!"
diff --git a/tests/InMemoryDocumentStoreTest.php b/tests/InMemoryDocumentStoreTest.php
index ba03c86..641e112 100644
--- a/tests/InMemoryDocumentStoreTest.php
+++ b/tests/InMemoryDocumentStoreTest.php
@@ -119,7 +119,32 @@ public function it_ensures_unique_constraints_for_a_field()
         $this->store->addDoc('test', '3', ['some' => ['prop' => 'foo']]);
     }
 
+    /**
+     * @test
+     */
+    public function it_ensures_unique_constraints_for_a_field_for_update()
+    {
+        $this->store->addCollection('test', FieldIndex::namedIndexForField('unique_prop_idx', 'some.prop', FieldIndex::SORT_ASC, true));
+
+        $this->store->addDoc('test', '1', ['some' => ['prop' => 'foo']]);
+        $this->store->addDoc('test', '2', ['some' => ['prop' => 'bar']]);
+
+        $this->expectExceptionMessageRegExp('/^Unique constraint violation/');
+        $this->store->updateDoc('test', '2', ['some' => ['prop' => 'foo']]);
+    }
 
+    /**
+     * @test
+     * @doesNotPerformAssertions
+     */
+    public function it_allows_updating_with_unique_constraints_for_a_field()
+    {
+        $this->store->addCollection('test', FieldIndex::namedIndexForField('unique_prop_idx', 'some.prop', FieldIndex::SORT_ASC, true));
+
+        $this->store->addDoc('test', '1', ['some' => ['prop' => 'foo']]);
+
+        $this->store->updateDoc('test', '1', ['some' => ['prop' => 'foo', 'new' => 'prop']]);
+    }
 
     /**
      * @test
@@ -130,6 +155,22 @@ public function it_ensures_unique_constraints_for_multiple_fields()
 
         $this->store->addCollection('test', $multiFieldIndex);
 
+        $this->store->addDoc('test', '1', ['some' => ['prop' => 'foo', 'other' => ['prop' => 'bat']]]);
+        $this->store->addDoc('test', '2', ['some' => ['prop' => 'bar', 'other' => ['prop' => 'bat']]]);
+
+        $this->expectExceptionMessageRegExp('/^Unique constraint violation/');
+        $this->store->addDoc('test', '4', ['some' => ['prop' => 'foo', 'other' => ['prop' => 'bat']]]);
+    }
+
+    /**
+     * @test
+     */
+    public function it_ensures_unique_constraints_for_multiple_fields_for_update()
+    {
+        $multiFieldIndex = MultiFieldIndex::forFields(['some.prop', 'some.other.prop'], true);
+
+        $this->store->addCollection('test', $multiFieldIndex);
+
         $this->store->addDoc('test', '1', ['some' => ['prop' => 'foo', 'other' => ['prop' => 'bat']]]);
         $this->store->addDoc('test', '2', ['some' => ['prop' => 'bar', 'other' => ['prop' => 'bat']]]);
         $this->store->addDoc('test', '3', ['some' => ['prop' => 'bar']]);
@@ -138,6 +179,21 @@ public function it_ensures_unique_constraints_for_multiple_fields()
         $this->store->updateDoc('test', '2', ['some' => ['prop' => 'foo']]);
     }
 
+    /**
+     * @test
+     * @doesNotPerformAssertions
+     */
+    public function it_allows_updating_with_unique_constraints_for_multiple_fields()
+    {
+        $multiFieldIndex = MultiFieldIndex::forFields(['some.prop', 'some.other.prop'], true);
+
+        $this->store->addCollection('test', $multiFieldIndex);
+
+        $this->store->addDoc('test', '1', ['some' => ['prop' => 'foo', 'other' => ['prop' => 'bat']]]);
+
+        $this->store->updateDoc('test', '1', ['some' => ['prop' => 'foo', 'other' => ['prop' => 'bat'], 'new' => 'prop']]);
+    }
+
     /**
      * @test
      */