diff --git a/src/frequenz/client/reporting/_client.py b/src/frequenz/client/reporting/_client.py
index ee0a8dd..f34167f 100644
--- a/src/frequenz/client/reporting/_client.py
+++ b/src/frequenz/client/reporting/_client.py
@@ -95,7 +95,7 @@ def iterate_metric_samples(self) -> Generator[MetricSample, None, None]:
                     )
 
     @property
-    def next_page_token(self) -> Any:
+    def next_page_token(self) -> str | None:
         """Get the token for the next page of data.
 
         Returns: