diff --git a/src/Analyze/Result/EntityResult.php b/src/Analyze/Result/EntityResult.php
index 4f59c36..8e52aa7 100644
--- a/src/Analyze/Result/EntityResult.php
+++ b/src/Analyze/Result/EntityResult.php
@@ -21,4 +21,12 @@ readonly class EntityResult
         public array $fields,
         public EntityField $idField
     ) {}
+
+    /**
+     * @return list<EntityField>
+     */
+    public function fieldsWithoutId(): array
+    {
+        return array_filter($this->fields, static fn(EntityField $field) => !$field->isIdField);
+    }
 }
diff --git a/src/Repository/ResolutionStrategy/Execution/UpdateEntity.php b/src/Repository/ResolutionStrategy/Execution/UpdateEntity.php
new file mode 100644
index 0000000..f9010d7
--- /dev/null
+++ b/src/Repository/ResolutionStrategy/Execution/UpdateEntity.php
@@ -0,0 +1,66 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Kartierung\Repository\ResolutionStrategy\Execution;
+
+use Kartierung\Analyze\Result\EntityField;
+use Kartierung\Analyze\Result\EntityResult;
+use Kartierung\Repository\InvalidCall;
+use PDO;
+
+readonly class UpdateEntity
+{
+    public function __construct(
+        private PDO $pdo
+    ) {}
+
+    /**
+     * @param EntityResult<object> $entityResult
+     * @param array<string, mixed> $data
+     * @return object
+     */
+    public function update(EntityResult $entityResult, array $data): object
+    {
+        $pairs = implode(', ', array_map(
+            static fn(EntityField $field) => "$field->columnName = ?",
+            $entityResult->fieldsWithoutId()
+        ));
+        $idWhere = $entityResult->idField->columnName . ' = ?';
+
+        $params = array_map(
+            static fn(EntityField $field) => $data[$field->columnName] ?? null,
+            $entityResult->fieldsWithoutId()
+        );
+        $id = $data[$entityResult->idField->columnName] ?? null;
+        $params[] = $id;
+        // reindex keys for pdo
+        $params = array_values($params);
+
+        $sql = "UPDATE $entityResult->tableName SET $pairs WHERE $idWhere";
+        $prepStmt = $this->pdo->prepare($sql);
+        $success = $prepStmt->execute($params);
+
+        if (!$success) {
+            throw new InvalidCall(
+                "Database reports failed updated statement."
+            );
+        }
+
+        $rows = $prepStmt->rowCount();
+        if ($rows !== 1) {
+            throw new InvalidCall(
+                "Database returns $rows affected. Exactly 1 expected."
+            );
+        }
+
+        $entity = (new SelectEntityById($this->pdo))->select($entityResult, $id);
+        if (!$entity) {
+            throw new InvalidCall(
+                "Entity of type $entityResult->classFqcn with id $id can not be selected."
+            );
+        }
+
+        return $entity;
+    }
+}
diff --git a/src/Repository/ResolutionStrategy/SaveEntity.php b/src/Repository/ResolutionStrategy/SaveEntity.php
index fbd7993..e894d3f 100644
--- a/src/Repository/ResolutionStrategy/SaveEntity.php
+++ b/src/Repository/ResolutionStrategy/SaveEntity.php
@@ -10,6 +10,7 @@ use Kartierung\Analyze\Result\RepositoryMethod;
 use Kartierung\Analyze\Result\RepositoryMethodParameter;
 use Kartierung\Repository\InvalidCall;
 use Kartierung\Repository\ResolutionStrategy\Execution\InsertEntity;
+use Kartierung\Repository\ResolutionStrategy\Execution\UpdateEntity;
 use Kartierung\Sql\LazyQuery;
 use PDO;
 
@@ -18,7 +19,7 @@ class SaveEntity implements ResolutionStrategy
     public function createQuery(RepositoryMethod $method, array $parameters): LazyQuery
     {
         return new LazyQuery(
-            function (PDO $pdo) use ($method, $parameters): object|int {
+            function (PDO $pdo) use ($method, $parameters): object {
                 /** @var RepositoryMethodParameter $firstDeclaredParam */
                 $firstDeclaredParam = array_first($method->parameters);
                 /** @var object $firstParam */
@@ -39,7 +40,7 @@ class SaveEntity implements ResolutionStrategy
                 $entityData = (new EntityToDataMapper())->byColumnName($entityResult, $firstParam);
 
                 if ($this->hasIdValue($entityResult, $entityData)) {
-                    return $this->update();
+                    return $this->update($pdo, $entityResult, $entityData);
                 }
 
                 return $this->insert($pdo, $entityResult, $entityData);
@@ -47,9 +48,15 @@ class SaveEntity implements ResolutionStrategy
         );
     }
 
-    private function update(): int
+    /**
+     * @param PDO $pdo
+     * @param EntityResult<object> $entityResult
+     * @param array<string, mixed> $data
+     * @return object
+     */
+    private function update(PDO $pdo, EntityResult $entityResult, array $data): object
     {
-        return 0;
+        return (new UpdateEntity($pdo))->update($entityResult, $data);
     }
 
     /**
diff --git a/tests/Repository/ResolutionStrategy/SaveEntityTest.php b/tests/Repository/ResolutionStrategy/SaveEntityTest.php
index d6bb06e..7570322 100644
--- a/tests/Repository/ResolutionStrategy/SaveEntityTest.php
+++ b/tests/Repository/ResolutionStrategy/SaveEntityTest.php
@@ -7,6 +7,7 @@ namespace Kartierung\Repository\ResolutionStrategy;
 use Kartierung\Analyze\Result\ParameterFunction;
 use Kartierung\Analyze\Result\RepositoryMethod;
 use Kartierung\Analyze\Result\RepositoryMethodParameter;
+use PDO;
 use PHPUnit\Framework\Attributes\Group;
 
 class SaveEntityTest extends SqliteBaseCase
@@ -29,7 +30,7 @@ class SaveEntityTest extends SqliteBaseCase
     }
 
     #[Group('integration')]
-    public function testSelectsData(): void
+    public function testCreatesNewEntity(): void
     {
         // Given
         $strategy = new SaveEntity();
@@ -57,6 +58,51 @@ class SaveEntityTest extends SqliteBaseCase
         // Then
         $this->assertInstanceOf(SimpleEntity::class, $result);
         $this->assertNotNull($result->intcol);
+        $this->assertNotSame($result, $entity);
+
+        $stmt = $this->getPdo()->query("SELECT COUNT(*) c FROM SimpleEntity");
+        $row = $stmt->fetch(PDO::FETCH_ASSOC);
+        $this->assertEquals(3, $row['c'], 'Three rows expected');
+    }
+
+    #[Group('integration')]
+    public function testUpdatesEntity(): void
+    {
+        // Given
+        $strategy = new SaveEntity();
+        $method = new RepositoryMethod(
+            query: '',
+            returnType: '',
+            returnsNullable: true,
+            returnListType: '',
+            name: '',
+            parameters: [
+                new RepositoryMethodParameter(
+                    name: '',
+                    type: SimpleEntity::class,
+                    function: ParameterFunction::STATEMENT_PARAMETER
+                )
+            ],
+            resolutionStrategy: $strategy
+        );
+        $entity = new SimpleEntity(1, 'foobar');
+        $query = $method->createQuery([$entity]);
+
+        // When
+        $result = $query->execute($this->getPdo());
+
+        // Then
+        $this->assertInstanceOf(SimpleEntity::class, $result);
+        $this->assertNotSame($result, $entity);
+        $this->assertEquals($entity, $result);
+
+        $stmt = $this->getPdo()->query("SELECT COUNT(*) c FROM SimpleEntity");
+        $row = $stmt->fetch(PDO::FETCH_ASSOC);
+        $this->assertEquals(2, $row['c'], 'Three rows expected');
+
+        $stmt = $this->getPdo()->query('SELECT stringcol c FROM SimpleEntity WHERE intcol = 1');
+        $row = $stmt->fetch(PDO::FETCH_ASSOC);
+        $this->assertEquals('foobar', $row['c']);
     }
 
 }