diff --git a/src/burn/drv/pre90s/d_mustache.cpp b/src/burn/drv/pre90s/d_mustache.cpp
index 3de95fbf9..b4a74ac52 100644
--- a/src/burn/drv/pre90s/d_mustache.cpp
+++ b/src/burn/drv/pre90s/d_mustache.cpp
@@ -113,7 +113,7 @@ static struct BurnDIPInfo MustacheDIPList[]=
 
 STDDIPINFO(Mustache)
 
-UINT8 __fastcall mustache_main_read(UINT16 a)
+static UINT8 __fastcall mustache_main_read(UINT16 a)
 {
 	switch (a)
 	{
@@ -139,7 +139,7 @@ UINT8 __fastcall mustache_main_read(UINT16 a)
 	return 0;
 }
 
-void __fastcall mustache_main_write(UINT16 a, UINT8 d)
+static void __fastcall mustache_main_write(UINT16 a, UINT8 d)
 {
 	switch (a)
 	{