diff --git a/src/Client/Client.php b/src/Client/Client.php
index 427870d..ad8279e 100644
--- a/src/Client/Client.php
+++ b/src/Client/Client.php
@@ -246,6 +246,8 @@ public function update(UpdateInput $input): bool
      *
      * @param UpsertInput<Entity> $input
      *
+     * @phpstan-impure - it writes, so the next call with the same input can have another outcome
+     *
      * @throws UnknownEntityDefinitionException
      * @throws ConditionEmptyException
      * @throws UpdateEmptyException if the update has nothing to write