diff --git a/libs/backends/portaudio/winmmemidi_io.h b/libs/backends/portaudio/winmmemidi_io.h
index a2868241d8..28450e95cb 100644
--- a/libs/backends/portaudio/winmmemidi_io.h
+++ b/libs/backends/portaudio/winmmemidi_io.h
@@ -23,6 +23,7 @@
 #include <vector>
 #include <string>
 #include <stdint.h>
+#include <pthread.h>
 
 #include <boost/shared_ptr.hpp>
 #include "pbd/ringbuffer.h"
diff --git a/libs/backends/portaudio/winmmemidi_output_device.h b/libs/backends/portaudio/winmmemidi_output_device.h
index ead85d7169..8c4d4d0c90 100644
--- a/libs/backends/portaudio/winmmemidi_output_device.h
+++ b/libs/backends/portaudio/winmmemidi_output_device.h
@@ -23,6 +23,7 @@
 #include <mmsystem.h>
 
 #include <stdint.h>
+#include <pthread.h>
 
 #include <string>