diff --git a/src/sound/null_s.cpp b/src/sound/null_s.cpp
--- a/src/sound/null_s.cpp
+++ b/src/sound/null_s.cpp
@@ -12,4 +12,5 @@
 #include "../stdafx.h"
 #include "null_s.h"
 
+/** The factory for the null sound driver. */
 static FSoundDriver_Null iFSoundDriver_Null;