diff --git a/datastore/query.go b/datastore/query.go
index 5851662..f2e6d9c 100644
--- a/datastore/query.go
+++ b/datastore/query.go
@@ -594,6 +594,8 @@
 }
 
 // Iterator is the result of running a query.
+//
+// It is not safe for concurrent use.
 type Iterator struct {
 	ctx    context.Context
 	client *Client