diff --git a/proxy/blackhole/config_json_test.go b/proxy/blackhole/config_json_test.go
index a61537eaa..b9094a940 100644
--- a/proxy/blackhole/config_json_test.go
+++ b/proxy/blackhole/config_json_test.go
@@ -1,3 +1,5 @@
+// +build json
+
 package blackhole_test
 
 import (