diff --git a/gumble/gumble/udp15.go b/gumble/gumble/udp15.go
index 1132c53..a91b7ec 100644
--- a/gumble/gumble/udp15.go
+++ b/gumble/gumble/udp15.go
@@ -412,6 +412,8 @@ var udp15Client *cryptState15
 var udp15Server *cryptState15
 
 // SetUDP15Crypto installs the 1.5 native UDP crypto state from CryptSetup.
+// udp15Client: encrypts with client_nonce (outbound).
+// udp15Server: decrypts with server_nonce (inbound).
 func SetUDP15Crypto(key, clientNonce, serverNonce []byte) {
 	csClient := &cryptState15{}
 	if err := csClient.setup15(key, clientNonce, serverNonce); err != nil {
@@ -420,11 +422,12 @@ func SetUDP15Crypto(key, clientNonce, serverNonce []byte) {
 	}
 	udp15Client = csClient
 
+	// Server state: we only use decryptIV (to decrypt server→client packets).
+	// The server encrypts with server_nonce, so our decryptIV must be server_nonce.
 	csServer := &cryptState15{}
-	if err := csServer.setup15(key, serverNonce, clientNonce); err != nil {
-		log.Error("SetUDP15Crypto server: %v", err)
-		return
-	}
+	copy(csServer.key[:], key)
+	copy(csServer.decryptIV[:], serverNonce)
+	csServer.initialized = true
 	udp15Server = csServer
 
 	log.Info("Mumble 1.5 native UDP crypto initialized")