diff --git a/docs/class-reference.md b/docs/class-reference.md
index 70947cdff..38f6990be 100644
--- a/docs/class-reference.md
+++ b/docs/class-reference.md
@@ -76,6 +76,8 @@ static function executeQuery(
  * @param array<string, mixed>|null  $variableValues
  * @param array<ValidationRule>|null $validationRules
  *
+ * @return Promise<ExecutionResult>
+ *
  * @api
  */
 static function promiseToExecute(
@@ -1305,6 +1307,8 @@ static function execute(
  * @param mixed                     $contextValue
  * @param array<string, mixed>|null $variableValues
  *
+ * @return Promise<ExecutionResult>
+ *
  * @phpstan-param FieldResolver|null $fieldResolver
  *
  * @api
@@ -1457,7 +1461,11 @@ function isThenable($value): bool
 /**
  * Converts thenable of the underlying platform into GraphQL\Executor\Promise\Promise instance.
  *
- * @param mixed $thenable
+ * @template T
+ *
+ * @param T $thenable
+ *
+ * @return Promise<T>
  *
  * @api
  */
@@ -1466,8 +1474,22 @@ function convertThenable($thenable): GraphQL\Executor\Promise\Promise
 
 ```php
 /**
- * Accepts our Promise wrapper, extracts adopted promise out of it and executes actual `then` logic described
- * in Promises/A+ specs. Then returns new wrapped instance of GraphQL\Executor\Promise\Promise.
+ * Accepts our Promise wrapper, extracts adopted promise out of it and executes actual `then` logic described in Promises/A+ specs.
+ * Then returns new wrapped instance of @see \GraphQL\Executor\Promise\Promise.
+ *
+ * @template T
+ * @template TFulfilled of mixed
+ * @template TRejected of mixed
+ *
+ * @param Promise<T> $promise
+ * @param (callable(T): (Promise<TFulfilled>|TFulfilled))|null $onFulfilled
+ * @param (callable(\Throwable): (Promise<TRejected>|TRejected))|null $onRejected
+ *
+ * @return Promise<(
+ *   $onFulfilled is not null
+ *     ? ($onRejected is not null ? TFulfilled|TRejected : TFulfilled)
+ *     : ($onRejected is not null ? TRejected : T)
+ * )>
  *
  * @api
  */
@@ -1482,7 +1504,11 @@ function then(
 /**
  * Creates a Promise from the given resolver callable.
  *
- * @param callable(callable $resolve, callable $reject): void $resolver
+ * @template V
+ *
+ * @param callable(callable(V): void $resolve, callable(\Throwable): void $reject): void $resolver
+ *
+ * @return Promise<V>
  *
  * @api
  */
@@ -1493,7 +1519,11 @@ function create(callable $resolver): GraphQL\Executor\Promise\Promise
 /**
  * Creates a fulfilled Promise for a value if the value is not a promise.
  *
- * @param mixed $value
+ * @template V
+ *
+ * @param V $value
+ *
+ * @return Promise<V>
  *
  * @api
  */
@@ -1506,6 +1536,8 @@ function createFulfilled($value = null): GraphQL\Executor\Promise\Promise
  *
  * If the provided reason is a promise, then it is returned as-is.
  *
+ * @return Promise<null>
+ *
  * @api
  */
 function createRejected(Throwable $reason): GraphQL\Executor\Promise\Promise
@@ -1516,7 +1548,11 @@ function createRejected(Throwable $reason): GraphQL\Executor\Promise\Promise
  * Given an iterable of promises (or values), returns a promise that is fulfilled when all the
  * items in the iterable are fulfilled.
  *
- * @param iterable<Promise|mixed> $promisesOrValues
+ * @template V
+ *
+ * @param iterable<V> $promisesOrValues
+ *
+ * @return Promise<array<V>>
  *
  * @api
  */
@@ -1874,7 +1910,7 @@ function handleRequest($parsedBody = null): void
  *
  * @param OperationParams|array<OperationParams> $parsedBody
  *
- * @return ExecutionResult|array<int, ExecutionResult>|Promise
+ * @return ExecutionResult|array<ExecutionResult>|Promise<ExecutionResult>|Promise<array<ExecutionResult>>
  *
  * @api
  */
@@ -1888,7 +1924,7 @@ function executeRequest($parsedBody = null)
  * See `executePsrRequest()` if you prefer to create response yourself
  * (e.g. using specific JsonResponse instance of some framework).
  *
- * @return ResponseInterface|Promise
+ * @return ResponseInterface|Promise<ResponseInterface>
  *
  * @api
  */
@@ -1904,7 +1940,7 @@ function processPsrRequest(
  * Executes GraphQL operation and returns execution result
  * (or promise when promise adapter is different from SyncPromiseAdapter).
  *
- * @return ExecutionResult|array<int, ExecutionResult>|Promise
+ * @return ExecutionResult|array<ExecutionResult>|Promise<ExecutionResult>|Promise<array<ExecutionResult>>
  *
  * @api
  */
@@ -2116,7 +2152,7 @@ function validateOperationParams(GraphQL\Server\OperationParams $params): array
  * Executes GraphQL operation with given server configuration and returns execution result
  * (or promise when promise adapter is different from SyncPromiseAdapter).
  *
- * @return ExecutionResult|Promise
+ * @return ExecutionResult|Promise<ExecutionResult>
  *
  * @api
  */
@@ -2130,7 +2166,7 @@ function executeOperation(GraphQL\Server\ServerConfig $config, GraphQL\Server\Op
  *
  * @param array<OperationParams> $operations
  *
- * @return array<int, ExecutionResult>|Promise
+ * @return array<ExecutionResult>|Promise<array<ExecutionResult>>
  *
  * @api
  */
@@ -2141,7 +2177,7 @@ function executeBatch(GraphQL\Server\ServerConfig $config, array $operations)
 /**
  * Send response using standard PHP `header()` and `echo`.
  *
- * @param Promise|ExecutionResult|array<ExecutionResult> $result
+ * @param Promise<ExecutionResult>|Promise<array<ExecutionResult>>|ExecutionResult|array<ExecutionResult> $result
  *
  * @api
  */
@@ -2165,9 +2201,9 @@ function parsePsrRequest(Psr\Http\Message\RequestInterface $request)
 /**
  * Converts query execution result to PSR-7 response.
  *
- * @param Promise|ExecutionResult|array<ExecutionResult> $result
+ * @param Promise<ExecutionResult>|Promise<array<ExecutionResult>>|ExecutionResult|array<ExecutionResult> $result
  *
- * @return Promise|ResponseInterface
+ * @return Promise<ResponseInterface>|ResponseInterface
  *
  * @api
  */
diff --git a/src/Deferred.php b/src/Deferred.php
index d0f99ec13..73aa47fac 100644
--- a/src/Deferred.php
+++ b/src/Deferred.php
@@ -5,23 +5,21 @@
 use GraphQL\Executor\Promise\Adapter\SyncPromise;
 
 /**
- * @phpstan-import-type Executor from SyncPromise
+ * @template V
+ *
+ * @extends SyncPromise<V>
  */
 class Deferred extends SyncPromise
 {
     /**
-     * @param Executor $executor
+     * @template T
+     *
+     * @param callable(): T $executor
+     *
+     * @return self<T>
      */
     public static function create(callable $executor): self
     {
         return new self($executor);
     }
-
-    /**
-     * @param Executor $executor
-     */
-    public function __construct(callable $executor)
-    {
-        parent::__construct($executor);
-    }
 }
diff --git a/src/Executor/Executor.php b/src/Executor/Executor.php
index 88c132d2a..c652006b8 100644
--- a/src/Executor/Executor.php
+++ b/src/Executor/Executor.php
@@ -132,6 +132,8 @@ public static function execute(
      * @param mixed                     $contextValue
      * @param array<string, mixed>|null $variableValues
      *
+     * @return Promise<ExecutionResult>
+     *
      * @phpstan-param FieldResolver|null $fieldResolver
      *
      * @api
diff --git a/src/Executor/ExecutorImplementation.php b/src/Executor/ExecutorImplementation.php
index b614d8b73..b0e4726c2 100644
--- a/src/Executor/ExecutorImplementation.php
+++ b/src/Executor/ExecutorImplementation.php
@@ -8,6 +8,8 @@ interface ExecutorImplementation
 {
     /**
      * Returns promise of {@link ExecutionResult}. Promise should always resolve, never reject.
+     *
+     * @return Promise<ExecutionResult>
      */
     public function doExecute(): Promise;
 }
diff --git a/src/Executor/Promise/Adapter/SyncPromise.php b/src/Executor/Promise/Adapter/SyncPromise.php
index 36a41f3e1..9bd048c7d 100644
--- a/src/Executor/Promise/Adapter/SyncPromise.php
+++ b/src/Executor/Promise/Adapter/SyncPromise.php
@@ -15,7 +15,7 @@
  * The whole point of Deferred is to ensure it never happens and that any resolver creates
  * at least one $executor to start the promise chain.
  *
- * @phpstan-type Executor callable(): mixed
+ * @template V
  */
 class SyncPromise
 {
@@ -34,7 +34,7 @@ class SyncPromise
      * @var array<
      *     int,
      *     array{
-     *         self,
+     *         self<V>,
      *         (callable(mixed): mixed)|null,
      *         (callable(\Throwable): mixed)|null
      *     }
@@ -52,7 +52,7 @@ public static function runQueue(): void
     }
 
     /**
-     * @param Executor|null $executor
+     * @param (callable(): V)|null $executor
      */
     public function __construct(?callable $executor = null)
     {
@@ -71,6 +71,8 @@ public function __construct(?callable $executor = null)
 
     /**
      * @param mixed $value
+     *
+     * @return self<V>
      */
     public function resolve($value): self
     {
@@ -110,6 +112,9 @@ function ($reason): void {
         return $this;
     }
 
+    /**
+     * @return self<null>
+     */
     public function reject(\Throwable $reason): self
     {
         switch ($this->state) {
@@ -175,8 +180,17 @@ public static function getQueue(): \SplQueue
     }
 
     /**
-     * @param (callable(mixed): mixed)|null $onFulfilled
-     * @param (callable(\Throwable): mixed)|null $onRejected
+     * @template VFulfilled
+     * @template VRejected
+     *
+     * @param (callable(V): VFulfilled)|null $onFulfilled
+     * @param (callable(\Throwable): VRejected)|null $onRejected
+     *
+     * @return self<(
+     *   $onFulfilled is not null
+     *     ? ($onRejected is not null ? VFulfilled|VRejected : VFulfilled)
+     *     : ($onRejected is not null ? VRejected : V)
+     * )>
      */
     public function then(?callable $onFulfilled = null, ?callable $onRejected = null): self
     {
@@ -200,6 +214,8 @@ public function then(?callable $onFulfilled = null, ?callable $onRejected = null
 
     /**
      * @param callable(\Throwable): mixed $onRejected
+     *
+     * @return self<null>
      */
     public function catch(callable $onRejected): self
     {
diff --git a/src/Executor/Promise/Adapter/SyncPromiseAdapter.php b/src/Executor/Promise/Adapter/SyncPromiseAdapter.php
index 1852de96a..d47b44b1a 100644
--- a/src/Executor/Promise/Adapter/SyncPromiseAdapter.php
+++ b/src/Executor/Promise/Adapter/SyncPromiseAdapter.php
@@ -110,7 +110,13 @@ static function ($value) use (&$result, $index, &$count, &$resolveAllWhenFinishe
     /**
      * Synchronously wait when promise completes.
      *
-     * @return mixed
+     * @template V
+     *
+     * @param Promise<V> $promise
+     *
+     * @throws InvariantViolation
+     *
+     * @return V
      */
     public function wait(Promise $promise)
     {
@@ -141,6 +147,8 @@ public function wait(Promise $promise)
 
     /**
      * Execute just before starting to run promise completion.
+     *
+     * @param Promise<mixed> $promise
      */
     protected function beforeWait(Promise $promise): void
     {
@@ -148,6 +156,8 @@ protected function beforeWait(Promise $promise): void
 
     /**
      * Execute while running promise completion.
+     *
+     * @param Promise<mixed> $promise
      */
     protected function onWait(Promise $promise): void
     {
diff --git a/src/Executor/Promise/Promise.php b/src/Executor/Promise/Promise.php
index b0dbb0c7a..ec6224192 100644
--- a/src/Executor/Promise/Promise.php
+++ b/src/Executor/Promise/Promise.php
@@ -3,33 +3,43 @@
 namespace GraphQL\Executor\Promise;
 
 use Amp\Promise as AmpPromise;
-use GraphQL\Error\InvariantViolation;
 use GraphQL\Executor\Promise\Adapter\SyncPromise;
 use React\Promise\PromiseInterface as ReactPromise;
 
 /**
  * Convenience wrapper for promises represented by Promise Adapter.
+ *
+ * @template T
  */
 class Promise
 {
-    /** @var SyncPromise|ReactPromise|AmpPromise<mixed> */
+    /** @var SyncPromise<T>|ReactPromise|AmpPromise<T> */
     public $adoptedPromise;
 
     private PromiseAdapter $adapter;
 
     /**
-     * @param mixed $adoptedPromise
+     * @param SyncPromise<T>|ReactPromise|AmpPromise<T> $adoptedPromise
      */
     public function __construct($adoptedPromise, PromiseAdapter $adapter)
     {
-        if ($adoptedPromise instanceof self) {
-            throw new InvariantViolation('Expecting promise from adapted system, got ' . self::class);
-        }
-
         $this->adoptedPromise = $adoptedPromise;
         $this->adapter = $adapter;
     }
 
+    /**
+     * @template TFulfilled
+     * @template TRejected
+     *
+     * @param (callable(T): (Promise<TFulfilled>|TFulfilled))|null $onFulfilled
+     * @param (callable(mixed): (Promise<TRejected>|TRejected))|null $onRejected
+     *
+     * @return Promise<(
+     *   $onFulfilled is not null
+     *     ? ($onRejected is not null ? TFulfilled|TRejected : TFulfilled)
+     *     : ($onRejected is not null ? TRejected : T)
+     * )>
+     */
     public function then(?callable $onFulfilled = null, ?callable $onRejected = null): Promise
     {
         return $this->adapter->then($this, $onFulfilled, $onRejected);
diff --git a/src/Executor/Promise/PromiseAdapter.php b/src/Executor/Promise/PromiseAdapter.php
index a91ee243d..51cf1f9e5 100644
--- a/src/Executor/Promise/PromiseAdapter.php
+++ b/src/Executor/Promise/PromiseAdapter.php
@@ -19,15 +19,33 @@ public function isThenable($value): bool;
     /**
      * Converts thenable of the underlying platform into GraphQL\Executor\Promise\Promise instance.
      *
-     * @param mixed $thenable
+     * @template T
+     *
+     * @param T $thenable
+     *
+     * @return Promise<T>
      *
      * @api
      */
     public function convertThenable($thenable): Promise;
 
     /**
-     * Accepts our Promise wrapper, extracts adopted promise out of it and executes actual `then` logic described
-     * in Promises/A+ specs. Then returns new wrapped instance of GraphQL\Executor\Promise\Promise.
+     * Accepts our Promise wrapper, extracts adopted promise out of it and executes actual `then` logic described in Promises/A+ specs.
+     * Then returns new wrapped instance of @see \GraphQL\Executor\Promise\Promise.
+     *
+     * @template T
+     * @template TFulfilled of mixed
+     * @template TRejected of mixed
+     *
+     * @param Promise<T> $promise
+     * @param (callable(T): (Promise<TFulfilled>|TFulfilled))|null $onFulfilled
+     * @param (callable(\Throwable): (Promise<TRejected>|TRejected))|null $onRejected
+     *
+     * @return Promise<(
+     *   $onFulfilled is not null
+     *     ? ($onRejected is not null ? TFulfilled|TRejected : TFulfilled)
+     *     : ($onRejected is not null ? TRejected : T)
+     * )>
      *
      * @api
      */
@@ -36,7 +54,11 @@ public function then(Promise $promise, ?callable $onFulfilled = null, ?callable
     /**
      * Creates a Promise from the given resolver callable.
      *
-     * @param callable(callable $resolve, callable $reject): void $resolver
+     * @template V
+     *
+     * @param callable(callable(V): void $resolve, callable(\Throwable): void $reject): void $resolver
+     *
+     * @return Promise<V>
      *
      * @api
      */
@@ -45,7 +67,11 @@ public function create(callable $resolver): Promise;
     /**
      * Creates a fulfilled Promise for a value if the value is not a promise.
      *
-     * @param mixed $value
+     * @template V
+     *
+     * @param V $value
+     *
+     * @return Promise<V>
      *
      * @api
      */
@@ -56,6 +82,8 @@ public function createFulfilled($value = null): Promise;
      *
      * If the provided reason is a promise, then it is returned as-is.
      *
+     * @return Promise<null>
+     *
      * @api
      */
     public function createRejected(\Throwable $reason): Promise;
@@ -64,7 +92,11 @@ public function createRejected(\Throwable $reason): Promise;
      * Given an iterable of promises (or values), returns a promise that is fulfilled when all the
      * items in the iterable are fulfilled.
      *
-     * @param iterable<Promise|mixed> $promisesOrValues
+     * @template V
+     *
+     * @param iterable<V> $promisesOrValues
+     *
+     * @return Promise<array<V>>
      *
      * @api
      */
diff --git a/src/Executor/ReferenceExecutor.php b/src/Executor/ReferenceExecutor.php
index 7fb87153b..e83a4462b 100644
--- a/src/Executor/ReferenceExecutor.php
+++ b/src/Executor/ReferenceExecutor.php
@@ -100,8 +100,14 @@ public static function create(
 
         if (\is_array($exeContext)) {
             return new class($promiseAdapter->createFulfilled(new ExecutionResult(null, $exeContext))) implements ExecutorImplementation {
+                /**
+                 * @var Promise<ExecutionResult>
+                 */
                 private Promise $result;
 
+                /**
+                 * @param Promise<ExecutionResult> $result
+                 */
                 public function __construct(Promise $result)
                 {
                     $this->result = $result;
@@ -243,7 +249,7 @@ public function doExecute(): Promise
     /**
      * @param mixed $data
      *
-     * @return ExecutionResult|Promise
+     * @return ExecutionResult|Promise<ExecutionResult>
      */
     protected function buildResponse($data)
     {
@@ -269,7 +275,7 @@ protected function buildResponse($data)
      *
      * @param mixed $rootValue
      *
-     * @return array<mixed>|Promise|\stdClass|null
+     * @return array<mixed>|Promise<mixed|null>|\stdClass|null
      */
     protected function executeOperation(OperationDefinitionNode $operation, $rootValue)
     {
@@ -301,6 +307,8 @@ protected function executeOperation(OperationDefinitionNode $operation, $rootVal
 
     /**
      * @param mixed $error
+     *
+     * @return Promise<null>|null
      */
     public function onError($error): ?Promise
     {
@@ -509,7 +517,7 @@ protected function doesFragmentConditionMatch(Node $fragment, ObjectType $type):
      *
      * @phpstan-param Fields $fields
      *
-     * @return array<mixed>|Promise|\stdClass
+     * @return array<string, mixed>|Promise<array<string, mixed>>|\stdClass
      */
     protected function executeFieldsSerially(ObjectType $parentType, $rootValue, array $path, \ArrayObject $fields)
     {
@@ -702,7 +710,7 @@ protected function resolveFieldValueOrError(
      *
      * @param mixed                       $result
      *
-     * @return array<mixed>|Promise|\stdClass|null
+     * @return array<string, mixed>|Promise<array<string, mixed>>|\stdClass|null
      */
     protected function completeValueCatchingError(
         Type $returnType,
@@ -792,7 +800,7 @@ protected function handleFieldError($rawError, \ArrayObject $fieldNodes, array $
      * @throws Error
      * @throws \Throwable
      *
-     * @return array<mixed>|mixed|Promise|null
+     * @return array<mixed>|mixed|Promise<mixed|array<mixed>>|null
      */
     protected function completeValue(
         Type $returnType,
@@ -877,7 +885,11 @@ protected function isPromise($value): bool
      * Only returns the value if it acts like a Promise, i.e. has a "then" function,
      * otherwise returns null.
      *
-     * @param mixed $value
+     * @template V
+     *
+     * @param V $value
+     *
+     * @return Promise<V>|null
      */
     protected function getPromise($value): ?Promise
     {
@@ -931,7 +943,7 @@ function ($previous, $value) use ($callback) {
      *
      * @throws \Exception
      *
-     * @return array<mixed>|Promise|\stdClass
+     * @return array<mixed>|Promise<array<mixed>>|\stdClass
      */
     protected function completeListValue(
         ListOfType $returnType,
@@ -998,7 +1010,7 @@ protected function completeLeafValue(LeafType $returnType, &$result)
      *
      * @throws Error
      *
-     * @return array<mixed>|Promise|\stdClass
+     * @return array<string, mixed>|Promise<array<string, mixed>>|\stdClass
      */
     protected function completeAbstractValue(
         AbstractType $returnType,
@@ -1062,7 +1074,7 @@ protected function completeAbstractValue(
      * @param mixed|null $contextValue
      * @param AbstractType&Type $abstractType
      *
-     * @return Promise|Type|string|null
+     * @return Promise<Type|string|null>|Type|string|null
      */
     protected function defaultTypeResolver($value, $contextValue, ResolveInfo $info, AbstractType $abstractType)
     {
@@ -1121,7 +1133,7 @@ protected function defaultTypeResolver($value, $contextValue, ResolveInfo $info,
      *
      * @throws Error
      *
-     * @return array<mixed>|Promise|\stdClass
+     * @return array<string, mixed>|Promise<array<string, mixed>>|\stdClass
      */
     protected function completeObjectValue(
         ObjectType $returnType,
@@ -1194,7 +1206,7 @@ protected function invalidReturnTypeError(
      *
      * @throws Error
      *
-     * @return array<mixed>|Promise|\stdClass
+     * @return array<string, mixed>|Promise<array<string, mixed>>|\stdClass
      */
     protected function collectAndExecuteSubfields(
         ObjectType $returnType,
@@ -1249,7 +1261,7 @@ protected function collectSubFields(ObjectType $returnType, \ArrayObject $fieldN
      *
      * @phpstan-param Fields $fields
      *
-     * @return Promise|\stdClass|array<mixed>
+     * @return Promise<array<string, mixed>>|\stdClass|array<string, mixed>
      */
     protected function executeFields(ObjectType $parentType, $rootValue, array $path, \ArrayObject $fields)
     {
@@ -1303,7 +1315,9 @@ protected static function fixResultsIfEmptyArray($results)
      * Transform an associative array with Promises to a Promise which resolves to an
      * associative array where all Promises were resolved.
      *
-     * @param array<string, Promise|mixed> $assoc
+     * @param array<string, Promise<mixed>|mixed> $assoc
+     *
+     * @return Promise<array<string, mixed>>
      */
     protected function promiseForAssocArray(array $assoc): Promise
     {
diff --git a/src/GraphQL.php b/src/GraphQL.php
index bded57793..a2e42e038 100644
--- a/src/GraphQL.php
+++ b/src/GraphQL.php
@@ -109,6 +109,8 @@ public static function executeQuery(
      * @param array<string, mixed>|null  $variableValues
      * @param array<ValidationRule>|null $validationRules
      *
+     * @return Promise<ExecutionResult>
+     *
      * @api
      */
     public static function promiseToExecute(
diff --git a/src/Server/Helper.php b/src/Server/Helper.php
index a4cb799ba..5f3ee02b6 100644
--- a/src/Server/Helper.php
+++ b/src/Server/Helper.php
@@ -172,7 +172,7 @@ public function validateOperationParams(OperationParams $params): array
      * Executes GraphQL operation with given server configuration and returns execution result
      * (or promise when promise adapter is different from SyncPromiseAdapter).
      *
-     * @return ExecutionResult|Promise
+     * @return ExecutionResult|Promise<ExecutionResult>
      *
      * @api
      */
@@ -194,7 +194,7 @@ public function executeOperation(ServerConfig $config, OperationParams $op)
      *
      * @param array<OperationParams> $operations
      *
-     * @return array<int, ExecutionResult>|Promise
+     * @return array<ExecutionResult>|Promise<array<ExecutionResult>>
      *
      * @api
      */
@@ -217,6 +217,9 @@ public function executeBatch(ServerConfig $config, array $operations)
         return $result;
     }
 
+    /**
+     * @return Promise<ExecutionResult>
+     */
     protected function promiseToExecuteOperation(
         PromiseAdapter $promiseAdapter,
         ServerConfig $config,
@@ -389,7 +392,7 @@ protected function resolveContextValue(
     /**
      * Send response using standard PHP `header()` and `echo`.
      *
-     * @param Promise|ExecutionResult|array<ExecutionResult> $result
+     * @param Promise<ExecutionResult>|Promise<array<ExecutionResult>>|ExecutionResult|array<ExecutionResult> $result
      *
      * @api
      */
@@ -513,9 +516,9 @@ protected function assertJsonObjectOrArray($bodyParams): void
     /**
      * Converts query execution result to PSR-7 response.
      *
-     * @param Promise|ExecutionResult|array<ExecutionResult> $result
+     * @param Promise<ExecutionResult>|Promise<array<ExecutionResult>>|ExecutionResult|array<ExecutionResult> $result
      *
-     * @return Promise|ResponseInterface
+     * @return Promise<ResponseInterface>|ResponseInterface
      *
      * @api
      */
diff --git a/src/Server/StandardServer.php b/src/Server/StandardServer.php
index ede83407c..ea1f8c22e 100644
--- a/src/Server/StandardServer.php
+++ b/src/Server/StandardServer.php
@@ -90,7 +90,7 @@ public function handleRequest($parsedBody = null): void
      *
      * @param OperationParams|array<OperationParams> $parsedBody
      *
-     * @return ExecutionResult|array<int, ExecutionResult>|Promise
+     * @return ExecutionResult|array<ExecutionResult>|Promise<ExecutionResult>|Promise<array<ExecutionResult>>
      *
      * @api
      */
@@ -113,7 +113,7 @@ public function executeRequest($parsedBody = null)
      * See `executePsrRequest()` if you prefer to create response yourself
      * (e.g. using specific JsonResponse instance of some framework).
      *
-     * @return ResponseInterface|Promise
+     * @return ResponseInterface|Promise<ResponseInterface>
      *
      * @api
      */
@@ -131,7 +131,7 @@ public function processPsrRequest(
      * Executes GraphQL operation and returns execution result
      * (or promise when promise adapter is different from SyncPromiseAdapter).
      *
-     * @return ExecutionResult|array<int, ExecutionResult>|Promise
+     * @return ExecutionResult|array<ExecutionResult>|Promise<ExecutionResult>|Promise<array<ExecutionResult>>
      *
      * @api
      */
diff --git a/src/Type/Definition/AbstractType.php b/src/Type/Definition/AbstractType.php
index c646b8805..754b501ed 100644
--- a/src/Type/Definition/AbstractType.php
+++ b/src/Type/Definition/AbstractType.php
@@ -5,7 +5,7 @@
 use GraphQL\Deferred;
 
 /**
- * @phpstan-type ResolveTypeReturn ObjectType|string|callable(): (ObjectType|string|null)|Deferred|null
+ * @phpstan-type ResolveTypeReturn ObjectType|string|callable(): ObjectType|string|null|Deferred<ObjectType|string|null>
  * @phpstan-type ResolveType callable(mixed $objectValue, mixed $context, ResolveInfo $resolveInfo): ResolveTypeReturn
  */
 interface AbstractType
@@ -16,7 +16,7 @@ interface AbstractType
      * @param mixed $objectValue The resolved value for the object type
      * @param mixed $context The context that was passed to GraphQL::execute()
      *
-     * @return ObjectType|string|callable|Deferred|null
+     * @return ObjectType|string|callable|Deferred<ObjectType|string|null>|null
      *
      * @phpstan-return ResolveTypeReturn
      */
diff --git a/src/Type/Definition/ObjectType.php b/src/Type/Definition/ObjectType.php
index 9c2d72efe..3025196a7 100644
--- a/src/Type/Definition/ObjectType.php
+++ b/src/Type/Definition/ObjectType.php
@@ -57,7 +57,7 @@
  *   resolveField?: FieldResolver|null,
  *   fields: (callable(): iterable<mixed>)|iterable<mixed>,
  *   interfaces?: iterable<InterfaceTypeReference>|callable(): iterable<InterfaceTypeReference>,
- *   isTypeOf?: (callable(mixed $objectValue, mixed $context, ResolveInfo $resolveInfo): (bool|Deferred|null))|null,
+ *   isTypeOf?: (callable(mixed $objectValue, mixed $context, ResolveInfo $resolveInfo): (bool|null|Deferred<bool|null>))|null,
  *   astNode?: ObjectTypeDefinitionNode|null,
  *   extensionASTNodes?: array<int, ObjectTypeExtensionNode>|null
  * }
@@ -116,7 +116,7 @@ public static function assertObjectType($type): self
      * @param mixed $objectValue The resolved value for the object type
      * @param mixed $context     The context that was passed to GraphQL::execute()
      *
-     * @return bool|Deferred|null
+     * @return bool|Deferred<bool|null>|null
      */
     public function isTypeOf($objectValue, $context, ResolveInfo $info)
     {
diff --git a/tests/Executor/Promise/SyncPromiseAdapterTest.php b/tests/Executor/Promise/SyncPromiseAdapterTest.php
index b61860f6d..12bf7fb64 100644
--- a/tests/Executor/Promise/SyncPromiseAdapterTest.php
+++ b/tests/Executor/Promise/SyncPromiseAdapterTest.php
@@ -74,6 +74,9 @@ public function testCreatePromise(): void
     }
 
     /**
+     * @template T
+     *
+     * @param Promise<T> $promise
      * @param mixed $expectedNextValue
      */
     private static function assertValidPromise(Promise $promise, ?string $expectedNextReason, $expectedNextValue, string $expectedNextState): void
diff --git a/tests/Executor/Promise/SyncPromiseTest.php b/tests/Executor/Promise/SyncPromiseTest.php
index dafccbad1..3354925e5 100644
--- a/tests/Executor/Promise/SyncPromiseTest.php
+++ b/tests/Executor/Promise/SyncPromiseTest.php
@@ -137,6 +137,9 @@ static function () use (&$onRejectedCalled): void {
     }
 
     /**
+     * @template V
+     *
+     * @param SyncPromise<V> $promise
      * @param mixed $expectedNextValue
      */
     private static function assertValidPromise(
diff --git a/tests/Executor/SyncTest.php b/tests/Executor/SyncTest.php
index 1e245aa62..0ce8f6211 100644
--- a/tests/Executor/SyncTest.php
+++ b/tests/Executor/SyncTest.php
@@ -77,6 +77,8 @@ public function testDoesNotReturnAPromiseForInitialErrors(): void
 
     /**
      * @param mixed $rootValue
+     *
+     * @return Promise<ExecutionResult>
      */
     private function execute(Schema $schema, DocumentNode $doc, $rootValue = null): Promise
     {
@@ -85,6 +87,7 @@ private function execute(Schema $schema, DocumentNode $doc, $rootValue = null):
 
     /**
      * @param array<string, mixed> $expectedFinalArray
+     * @param Promise<ExecutionResult> $actualResult
      */
     private static function assertSync(array $expectedFinalArray, Promise $actualResult): void
     {
@@ -145,6 +148,7 @@ public function testReturnsAPromiseIfAnyFieldIsAsynchronous(): void
 
     /**
      * @param array<string, mixed> $expectedFinalArray
+     * @param Promise<ExecutionResult> $actualResult
      */
     private function assertAsync(array $expectedFinalArray, Promise $actualResult): void
     {
@@ -155,7 +159,6 @@ private function assertAsync(array $expectedFinalArray, Promise $actualResult):
         self::assertEquals(SyncPromise::PENDING, $adoptedPromise->state, $message);
 
         $resolvedResult = $this->promiseAdapter->wait($actualResult);
-        self::assertInstanceOf(ExecutionResult::class, $resolvedResult);
         self::assertArraySubset($expectedFinalArray, $resolvedResult->toArray());
     }
 
@@ -183,6 +186,8 @@ public function testDoesNotReturnAPromiseForSyntaxErrors(): void
 
     /**
      * @param mixed $rootValue
+     *
+     * @return Promise<ExecutionResult>
      */
     private function graphqlSync(Schema $schema, string $doc, $rootValue = null): Promise
     {
diff --git a/tests/Executor/TestClasses/Root.php b/tests/Executor/TestClasses/Root.php
index 9d192b127..e7ceed200 100644
--- a/tests/Executor/TestClasses/Root.php
+++ b/tests/Executor/TestClasses/Root.php
@@ -13,6 +13,9 @@ public function __construct(float $originalNumber)
         $this->numberHolder = new NumberHolder($originalNumber);
     }
 
+    /**
+     * @return Deferred<NumberHolder>
+     */
     public function promiseToChangeTheNumber(float $newNumber): Deferred
     {
         return new Deferred(fn (): NumberHolder => $this->immediatelyChangeTheNumber($newNumber));
@@ -30,6 +33,9 @@ public function failToChangeTheNumber(): void
         throw new \Exception('Cannot change the number');
     }
 
+    /**
+     * @return Deferred<void>
+     */
     public function promiseAndFailToChangeTheNumber(): Deferred
     {
         return new Deferred(function (): void {