diff --git a/client_server_httpsproxy_test.go b/client_server_httpsproxy_test.go
index 214ce33..71f0d55 100644
--- a/client_server_httpsproxy_test.go
+++ b/client_server_httpsproxy_test.go
@@ -1,3 +1,4 @@
+//go:build go1.15
 // +build go1.15
 
 package websocket
diff --git a/proxy_https.go b/proxy_https.go
index 3cc2baa..f74258a 100644
--- a/proxy_https.go
+++ b/proxy_https.go
@@ -1,3 +1,4 @@
+//go:build go1.15
 // +build go1.15
 
 package websocket
diff --git a/proxy_https_legacy.go b/proxy_https_legacy.go
index 461339e..40bc5e2 100644
--- a/proxy_https_legacy.go
+++ b/proxy_https_legacy.go
@@ -1,3 +1,4 @@
+//go:build !go1.15
 // +build !go1.15
 
 package websocket