diff --git a/cmd/contour/shutdownmanager.go b/cmd/contour/shutdownmanager.go
index 5d3f3c83a7b..37686339bb3 100644
--- a/cmd/contour/shutdownmanager.go
+++ b/cmd/contour/shutdownmanager.go
@@ -31,6 +31,8 @@ import (
 )
 
 const (
+	// The prometheusURL is used to fetch the envoy metrics. Note that the filter
+	// value matches Envoy's raw stat names (i.e. those on the `/stats/` endpoint).
 	prometheusURL      = "http://unix/stats/prometheus?filter=http\\..*\\.downstream_cx_active"
 	healthcheckFailURL = "http://unix/healthcheck/fail"
 	prometheusStat     = "envoy_http_downstream_cx_active"