diff --git a/internal/event/hclog_formatter_node.go b/internal/event/hclog_formatter_node.go
index 27affbb30a..60792c6a7b 100644
--- a/internal/event/hclog_formatter_node.go
+++ b/internal/event/hclog_formatter_node.go
@@ -205,6 +205,8 @@ func (f *hclogFormatterFilter) Process(ctx context.Context, e *eventlogger.Event
 	if err != nil {
 		return nil, fmt.Errorf("%s: unable to format: %w", op, err)
 	}
+	f.l.Lock()
+	defer f.l.Unlock()
 	if f.signer != nil && string(e.Type) == string(AuditType) {
 		bufHmac, err := f.signer(ctx, buf.Bytes())
 		if err != nil {