diff --git a/src/output/plugins/SndioOutputPlugin.cxx b/src/output/plugins/SndioOutputPlugin.cxx
index 285882665..1c74ed6c3 100644
--- a/src/output/plugins/SndioOutputPlugin.cxx
+++ b/src/output/plugins/SndioOutputPlugin.cxx
@@ -20,6 +20,7 @@
 #include "config.h"
 #include "SndioOutputPlugin.hxx"
 #include "mixer/MixerList.hxx"
+#include "mixer/Listener.hxx"
 #include "util/Domain.hxx"
 #include "Log.hxx"
 
diff --git a/src/output/plugins/SndioOutputPlugin.hxx b/src/output/plugins/SndioOutputPlugin.hxx
index 848918898..98d815594 100644
--- a/src/output/plugins/SndioOutputPlugin.hxx
+++ b/src/output/plugins/SndioOutputPlugin.hxx
@@ -18,11 +18,13 @@
  */
 
 #include "../OutputAPI.hxx"
-#include "mixer/Listener.hxx"
 
 #ifndef MPD_SNDIO_OUTPUT_PLUGIN_HXX
 #define MPD_SNDIO_OUTPUT_PLUGIN_HXX
 
+class Mixer;
+class MixerListener;
+
 extern const struct AudioOutputPlugin sndio_output_plugin;
 
 class SndioOutput final : AudioOutput {