diff --git a/conn.go b/conn.go
index af41beb..2701142 100644
--- a/conn.go
+++ b/conn.go
@@ -120,7 +120,7 @@ func maskBytes(key [4]byte, pos int, b []byte) int {
 
 func newMaskKey() [4]byte {
 	n := rand.Uint32()
-	return [4]byte{byte(n), byte(n >> 8), byte(n >> 16), byte(n >> 32)}
+	return [4]byte{byte(n), byte(n >> 8), byte(n >> 16), byte(n >> 24)}
 }
 
 // Conn represents a WebSocket connection.