diff --git a/src/output/MultipleOutputs.cxx b/src/output/MultipleOutputs.cxx
index 10c3f30b5..ee14abca8 100644
--- a/src/output/MultipleOutputs.cxx
+++ b/src/output/MultipleOutputs.cxx
@@ -172,7 +172,7 @@ MultipleOutputs::Update(bool force) noexcept
 {
 	bool ret = false;
 
-	if (!input_audio_format.IsDefined())
+	if (!IsOpen())
 		return false;
 
 	for (const auto &ao : outputs)
diff --git a/src/output/MultipleOutputs.hxx b/src/output/MultipleOutputs.hxx
index cc9b30d14..73e3ac00d 100644
--- a/src/output/MultipleOutputs.hxx
+++ b/src/output/MultipleOutputs.hxx
@@ -155,6 +155,15 @@ public:
 	void SetSoftwareVolume(unsigned volume) noexcept;
 
 private:
+	/**
+	 * Was Open() called successfully?
+	 *
+	 * This method may only be called from the player thread.
+	 */
+	bool IsOpen() const noexcept {
+		return input_audio_format.IsDefined();
+	}
+
 	/**
 	 * Wait until all (active) outputs have finished the current
 	 * command.