diff --git a/server/http_site_handler.go b/server/http_site_handler.go
index 84a326bcb..731f4456c 100644
--- a/server/http_site_handler.go
+++ b/server/http_site_handler.go
@@ -241,6 +241,7 @@ func healthHandler(site site.API) http.HandlerFunc {
 			return
 		}
 
+		w.Header().Set("Content-Type", "text/plain")
 		w.WriteHeader(http.StatusOK)
 		fmt.Fprintln(w, "OK")
 	}