diff --git a/pkg/causality/internal/node.go b/pkg/causality/internal/node.go
index 34d7574ea78..2d411f959fd 100644
--- a/pkg/causality/internal/node.go
+++ b/pkg/causality/internal/node.go
@@ -160,6 +160,8 @@ func (n *Node) Remove() {
 // It must be called if a node is no longer used.
 // We are using sync.Pool to lessen the burden of GC.
 func (n *Node) Free() {
+	n.mu.Lock()
+	defer n.mu.Unlock()
 	if n.id == invalidNodeID {
 		panic("double free")
 	}