diff --git a/pkl/evaluator.go b/pkl/evaluator.go
index e13183e..60f4f61 100644
--- a/pkl/evaluator.go
+++ b/pkl/evaluator.go
@@ -77,7 +77,7 @@ type evaluator struct {
 	logger          Logger
 	manager         *evaluatorManager
 	pendingRequests *sync.Map
-	closed          bool
+	closed          atomicBool
 	resourceReaders []ResourceReader
 	moduleReaders   []ModuleReader
 }
@@ -154,7 +154,7 @@ func (e *evaluator) EvaluateExpressionRaw(ctx context.Context, source *ModuleSou
 }
 
 func (e *evaluator) Close() error {
-	if e.closed {
+	if e.closed.get() {
 		return nil
 	}
 	e.manager.closeEvaluator(e)
@@ -162,7 +162,7 @@ func (e *evaluator) Close() error {
 }
 
 func (e *evaluator) Closed() bool {
-	return e.closed
+	return e.closed.get()
 }
 
 func (e *evaluator) handleEvaluateResponse(resp *msgapi.EvaluateResponse) {
diff --git a/pkl/evaluator_manager.go b/pkl/evaluator_manager.go
index 5fd57c6..3729f1a 100644
--- a/pkl/evaluator_manager.go
+++ b/pkl/evaluator_manager.go
@@ -273,7 +273,7 @@ func (m *evaluatorManager) closeEvaluator(ev *evaluator) {
 	}
 	m.impl.outChan() <- &msgapi.CloseEvaluator{EvaluatorId: ev.evaluatorId}
 	m.evaluators.Delete(ev.evaluatorId)
-	ev.closed = true
+	ev.closed.set(true)
 	m.interrupts.Range(func(key, value any) bool {
 		if value.(int64) == ev.evaluatorId {
 			key.(chan error) <- nil