diff --git a/gcs/builder/builder.go b/gcs/builder/builder.go
index d2bb8a1..e700b9e 100644
--- a/gcs/builder/builder.go
+++ b/gcs/builder/builder.go
@@ -15,6 +15,7 @@ import (
 	"github.com/btcsuite/btcutil/gcs"
 )
 
+// DefaultP is the default collision probability (2^-20)
 const DefaultP = 20
 
 // GCSBuilder is a utility class that makes building GCS filters convenient.