diff --git a/cart-grain.go b/cart-grain.go
index 2f71789..e069e01 100644
--- a/cart-grain.go
+++ b/cart-grain.go
@@ -111,7 +111,8 @@ func (c *CartGrain) AddItem(sku string, qty int) ([]byte, error) {
 }
 
 func (c *CartGrain) GetStorageMessage(since int64) []StorableMessage {
-
+	c.mu.RLock()
+	defer c.mu.RUnlock()
 	ret := make([]StorableMessage, 0)
 
 	for _, message := range c.storageMessages {