diff --git a/src/dosext/sound/sound.c b/src/dosext/sound/sound.c
index f33f78f..f429362 100644
--- a/src/dosext/sound/sound.c
+++ b/src/dosext/sound/sound.c
@@ -173,3 +173,3 @@ void sb_cms_write (ioport_t port, Bit8u value);
 
-inline void sb_mixer_register_write (Bit8u value);
+static inline void sb_mixer_register_write (Bit8u value);
 void sb_mixer_data_write (Bit8u value);
@@ -840,3 +840,3 @@ void sb_cms_write (ioport_t port, Bit8u value)
 
-inline void sb_mixer_register_write (Bit8u value)
+static inline void sb_mixer_register_write (Bit8u value)
 {