diff --git a/util_purego.go b/util_purego.go
index 4a8befd..449b3fd 100644
--- a/util_purego.go
+++ b/util_purego.go
@@ -1,4 +1,5 @@
 //go:build purego
+// +build purego
 
 package ws
 
diff --git a/util_unsafe.go b/util_unsafe.go
index 779f719..b732297 100644
--- a/util_unsafe.go
+++ b/util_unsafe.go
@@ -1,4 +1,5 @@
 //go:build !purego
+// +build !purego
 
 package ws