diff --git a/docs/en/observability/threshold-alert.asciidoc b/docs/en/observability/threshold-alert.asciidoc
index 202e7a6341..11beeae8b2 100644
--- a/docs/en/observability/threshold-alert.asciidoc
+++ b/docs/en/observability/threshold-alert.asciidoc
@@ -91,6 +91,8 @@ The shaded area shows the threshold you've set.
 [role="screenshot"]
 image::images/custom-threshold-preview-chart.png[Custom threshold preview chart,75%]
 
+If you use the **Group alerts by** option, the maximum bar size will be 3. It will only show the top 3 fields.
+
 [discrete]
 [[custom-threshold-group-by]]
 == Group alerts by (optional)