diff --git a/pkg/jsonconfig/eval.go b/pkg/jsonconfig/eval.go
index 9a24f9ff0..215ab54ab 100644
--- a/pkg/jsonconfig/eval.go
+++ b/pkg/jsonconfig/eval.go
@@ -61,7 +61,7 @@ type ConfigParser struct {
 	includeStack stringVector
 
 	// Open optionally specifies an opener function.
-	// TODO(bradfitz): define file.
+	// TODO(bradfitz): export/document the file type.
 	Open func(filename string) (file, error)
 }