diff --git a/src/output/Control.cxx b/src/output/Control.cxx
index ec0430a1e..2edcd7ca5 100644
--- a/src/output/Control.cxx
+++ b/src/output/Control.cxx
@@ -226,6 +226,7 @@ AudioOutputControl::Open(const AudioFormat audio_format,
 	const bool open2 = open;
 
 	if (open2 && output->mixer != nullptr) {
+		const ScopeUnlock unlock(mutex);
 		try {
 			mixer_open(output->mixer);
 		} catch (...) {
diff --git a/src/output/Thread.cxx b/src/output/Thread.cxx
index c8e90f726..3fb17ae54 100644
--- a/src/output/Thread.cxx
+++ b/src/output/Thread.cxx
@@ -501,5 +501,6 @@ AudioOutputControl::StartThread()
 {
 	assert(command == Command::NONE);
 
+	const ScopeUnlock unlock(mutex);
 	thread.Start();
 }