diff --git a/receivers/android/app/src/main/java/com/futo/fcast/receiver/FCastSession.kt b/receivers/android/app/src/main/java/com/futo/fcast/receiver/FCastSession.kt
index 8102cd8..dbe2b46 100644
--- a/receivers/android/app/src/main/java/com/futo/fcast/receiver/FCastSession.kt
+++ b/receivers/android/app/src/main/java/com/futo/fcast/receiver/FCastSession.kt
@@ -66,6 +66,8 @@ class FCastSession(outputStream: OutputStream, private val _remoteSocketAddress:
     val id = UUID.randomUUID()
 
     fun send(opcode: Opcode, message: String? = null) {
+        ensureNotMainThread()
+
         synchronized(_outputStreamLock) {
             try {
                 val data: ByteArray = message?.encodeToByteArray() ?: ByteArray(0)