diff --git a/common/sound_api.h b/common/sound_api.h
index 4c6034ab..77d6e58a 100644
--- a/common/sound_api.h
+++ b/common/sound_api.h
@@ -33,8 +33,17 @@ For more information, please refer to <http://unlicense.org/>
 
 #include "xash3d_types.h"
 
+// Experimental implementation, backward compatibility is not guaranteed.
 #define CL_SOUND_INTERFACE_VERSION	1
 
+#define FL_VOXWORD_IN_CACHE BIT( 0 ) // if set, it was loaded prior and shouldn't be freed
+
+#define FL_CHAN_USE_LOOP          BIT( 0 ) // don't loop default and local sounds
+#define FL_CHAN_STATIC_SOUND      BIT( 1 ) // use origin instead of fetching entnum's origin
+#define FL_CHAN_LOCAL_SOUND       BIT( 2 ) // it's a local menu sound (not looped, not paused)
+#define FL_CHAN_SENTENCE_FINISHED BIT( 4 ) // if set, finished playing sentence
+#define FL_CHAN_FINISHED          BIT( 5 ) // if set, finished playing single word
+
 typedef int sound_t;
 
 typedef struct portable_samplepair_s
diff --git a/engine/client/sound.h b/engine/client/sound.h
index 95eaebd7..4c8ea4c7 100644
--- a/engine/client/sound.h
+++ b/engine/client/sound.h
@@ -39,14 +39,6 @@ extern poolhandle_t sndpool;
 
 #define CLIP16( x ) bound( SHRT_MIN + 8, x, SHRT_MAX - 8 )
 
-#define FL_VOXWORD_IN_CACHE BIT( 0 ) // if set, it was loaded prior and shouldn't be freed
-
-#define FL_CHAN_USE_LOOP          BIT( 0 ) // don't loop default and local sounds
-#define FL_CHAN_STATIC_SOUND      BIT( 1 ) // use origin instead of fetching entnum's origin
-#define FL_CHAN_LOCAL_SOUND       BIT( 2 ) // it's a local menu sound (not looped, not paused)
-#define FL_CHAN_SENTENCE_FINISHED BIT( 4 ) // if set, finished playing sentence
-#define FL_CHAN_FINISHED          BIT( 5 ) // if set, finished playing single word
-
 //====================================================================
 
 #define MAX_DYNAMIC_CHANNELS (60 + NUM_AMBIENTS)