diff --git a/src/Factory/ActivityStub.php b/src/Factory/ActivityStub.php
index 3226a6f..537defa 100644
--- a/src/Factory/ActivityStub.php
+++ b/src/Factory/ActivityStub.php
@@ -59,6 +59,8 @@ final class ActivityStub
      *        completed, cancel accepted). {@see \Temporal\Activity\ActivityCancellationType}
      *
      * @return ($class is class-string ? T|ActivityProxy : ActivityStubInterface)
+     *
+     * @psalm-suppress LessSpecificReturnStatement,MoreSpecificReturnType
      */
     public static function activity(
         ?string $class = null,
@@ -98,7 +100,7 @@ public static function activity(
         $heartbeatTimeout === 0 or $options = $options->withHeartbeatTimeout($heartbeatTimeout);
         // Activity ID
         $activityId === null or $options = $options->withActivityId((string)$activityId);
-        $cancellationType === null or $options = $options->withCancellationType($cancellationType);
+        $cancellationType === 0 or $options = $options->withCancellationType($cancellationType);
 
         return $class === null
             ? Workflow::newUntypedActivityStub($options)
diff --git a/src/Factory/WorkflowStub.php b/src/Factory/WorkflowStub.php
index d2c58a1..f5f13e6 100644
--- a/src/Factory/WorkflowStub.php
+++ b/src/Factory/WorkflowStub.php
@@ -76,6 +76,8 @@ final class WorkflowStub
      * @param list<mixed> $memo Specifies additional non-indexed information in result of list workflow.
      *
      * @return ($type is class-string ? T|WorkflowProxy : WorkflowStubInterface)
+     *
+     * @psalm-suppress LessSpecificReturnStatement,MoreSpecificReturnType
      */
     public static function workflow(
         WorkflowClientInterface $workflowClient,
@@ -97,8 +99,11 @@ public static function workflow(
         array $searchAttributes = [],
         array $memo = [],
     ): object {
-        $isUntyped = !\class_exists($type) && !\interface_exists($type);
-        $attributes = $isUntyped ? new AttributeCollection([]) : self::readAttributes($type);
+        $isTyped = self::isClassOrInterface($type);
+        /** @psalm-suppress ArgumentTypeCoercion */
+        $attributes = $isTyped
+            ? self::readAttributes($type)
+            : new AttributeCollection([]);
 
         // Retry options
         $retryOptions = RetryOptions::create(
@@ -129,9 +134,10 @@ public static function workflow(
         $searchAttributes === [] or $options = $options->withSearchAttributes($searchAttributes);
         $memo === [] or $options = $options->withMemo($memo);
 
-        return $isUntyped
-            ? $workflowClient->newUntypedWorkflowStub($type, $options)
-            : $workflowClient->newWorkflowStub($type, $options);
+        /** @psalm-suppress ArgumentTypeCoercion */
+        return $isTyped
+            ? $workflowClient->newWorkflowStub($type, $options)
+            : $workflowClient->newUntypedWorkflowStub($type, $options);
     }
 
     /**
@@ -181,6 +187,8 @@ public static function workflow(
      * @param list<mixed> $memo Specifies additional non-indexed information in result of list workflow.
      *
      * @return ($type is class-string ? T|ChildWorkflowProxy : ChildWorkflowStubInterface)
+     *
+     * @psalm-suppress LessSpecificReturnStatement,MoreSpecificReturnType
      */
     public static function childWorkflow(
         string $type,
@@ -202,8 +210,11 @@ public static function childWorkflow(
         array $searchAttributes = [],
         array $memo = [],
     ): object {
-        $isUntyped = !\class_exists($type) && !\interface_exists($type);
-        $attributes = $isUntyped ? new AttributeCollection([]) : self::readAttributes($type);
+        $isTyped = self::isClassOrInterface($type);
+        /** @psalm-suppress ArgumentTypeCoercion */
+        $attributes = $isTyped
+            ? self::readAttributes($type)
+            : new AttributeCollection([]);
 
         // Retry options
         $retryOptions = RetryOptions::create(
@@ -239,9 +250,10 @@ public static function childWorkflow(
         $searchAttributes === [] or $options = $options->withSearchAttributes($searchAttributes);
         $memo === [] or $options = $options->withMemo($memo);
 
-        return $isUntyped
-            ? Workflow::newUntypedChildWorkflowStub($type, $options)
-            : Workflow::newChildWorkflowStub($type, $options);
+        /** @psalm-suppress ArgumentTypeCoercion */
+        return $isTyped
+            ? Workflow::newChildWorkflowStub($type, $options)
+            : Workflow::newUntypedChildWorkflowStub($type, $options);
     }
 
     /**
@@ -251,4 +263,14 @@ private static function readAttributes(string $class): AttributeCollection
     {
         return AttributeReader::collectionFromClass($class, [AttributeForWorkflow::class]);
     }
+
+    /**
+     * @param non-empty-string $type
+     * @psalm-assert-if-true class-string $type
+     * @psalm-assert-if-false non-empty-string $type
+     */
+    private static function isClassOrInterface(string $type): bool
+    {
+        return \class_exists($type) || \interface_exists($type);
+    }
 }
diff --git a/src/Internal/Attribute/AttributeCollection.php b/src/Internal/Attribute/AttributeCollection.php
index a95ecd2..86bb3d2 100644
--- a/src/Internal/Attribute/AttributeCollection.php
+++ b/src/Internal/Attribute/AttributeCollection.php
@@ -47,20 +47,19 @@ public function first(string $class): ?object
         return $result;
     }
 
-    public function has(string $class): bool
-    {
-        return $this->count($this->attributes[$class]) > 0;
-    }
-
     /**
+     * @param class-string $class
      * @return int<0, max>
      */
     public function count(string $class): int
     {
         $this->makeIndex($class);
-        return \count($this->attributes[$class]);
+        return \count($this->attributes[$class] ?? []);
     }
 
+    /**
+     * @param class-string $class
+     */
     private function makeIndex(string $class): void
     {
         if (\array_key_exists($class, $this->attributes)) {
diff --git a/src/Internal/Attribute/AttributeReader.php b/src/Internal/Attribute/AttributeReader.php
index 1267413..0f3c4fc 100644
--- a/src/Internal/Attribute/AttributeReader.php
+++ b/src/Internal/Attribute/AttributeReader.php
@@ -100,6 +100,9 @@ private static function fetchAttributes(\ReflectionClass $reflection, array $fil
         return $result;
     }
 
+    /**
+     * @return list<class-string>
+     */
     private static function sortInterfaces(\ReflectionClass $class): array
     {
         $result = [];
diff --git a/src/Internal/RetryOptions.php b/src/Internal/RetryOptions.php
index ca9c4b0..b1daa22 100644
--- a/src/Internal/RetryOptions.php
+++ b/src/Internal/RetryOptions.php
@@ -51,6 +51,7 @@ public static function create(
         $retryAttempts > 0 and $retryOptions = $retryOptions->withMaximumAttempts($retryAttempts);
         $retryInitInterval === null or $retryOptions = $retryOptions->withInitialInterval($retryInitInterval);
         $retryMaxInterval === null or $retryOptions = $retryOptions->withMaximumInterval($retryMaxInterval);
+        /** @psalm-suppress PossiblyNullArgument */
         $retryBackoff >= 1.0 and $retryOptions = $retryOptions->withBackoffCoefficient($retryBackoff);
         $nonRetryables === [] or $retryOptions = $retryOptions->withNonRetryableExceptions($nonRetryables);
         return $retryOptions;
diff --git a/src/VirtualPromise.php b/src/VirtualPromise.php
index bac8bbf..b0bca64 100644
--- a/src/VirtualPromise.php
+++ b/src/VirtualPromise.php
@@ -31,6 +31,8 @@
  *     }
  * }
  * ```
+ *
+ * @psalm-suppress TooManyTemplateParams
  */
 interface VirtualPromise extends PromiseInterface
 {