diff --git a/src/pcm/Traits.hxx b/src/pcm/Traits.hxx
index 48e7d559e..4e68191f6 100644
--- a/src/pcm/Traits.hxx
+++ b/src/pcm/Traits.hxx
@@ -24,6 +24,7 @@
 #include "AudioFormat.hxx"
 
 #include <stdint.h>
+#include <stddef.h>
 
 /**
  * This template describes the specified #SampleFormat.  This is an