diff --git a/src/FatFs/diskio.h b/src/FatFs/diskio.h
index 2fa4b280f..29a5cf88d 100644
--- a/src/FatFs/diskio.h
+++ b/src/FatFs/diskio.h
@@ -26,6 +26,10 @@ typedef enum {
 /*---------------------------------------*/
 /* Prototypes for disk control functions */
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 int assign_drives (int, int);
 DSTATUS disk_initialize (BYTE);
 DSTATUS disk_status (BYTE);
@@ -35,6 +39,9 @@ DRESULT disk_write (BYTE, const BYTE*, DWORD, BYTE);
 #endif
 DRESULT disk_ioctl (BYTE, BYTE, void*);
 
+#ifdef __cplusplus
+}
+#endif
 
 
 /* Disk Status Bits (DSTATUS) */
diff --git a/src/Makefile b/src/Makefile
index fc9b0499f..5df555df0 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -441,8 +441,9 @@ ifeq ($(PCB), X9D)
   CPPSRC += sky9x/sound_driver.cpp sky9x/haptic_driver.cpp sky9x/sdcard_driver.cpp
   
   ifeq ($(SDCARD), YES)
-    SRC += FatFs/ff.c FatFs/fattime.c FatFs/option/ccsbcs.c sky9x/diskio.c
+    EXTRABOARDSRC += FatFs/ff.c FatFs/fattime.c FatFs/option/ccsbcs.c sky9x/diskio.cpp
     CPPDEFS += -DVOICE
+    EXTRAINCDIRS += FatFs FatFs/option
   endif
   
   ifeq ($(BLUETOOTH), YES)
@@ -476,7 +477,8 @@ ifeq ($(PCB), SKY9X)
   CPPSRC += sky9x/sound_driver.cpp sky9x/haptic_driver.cpp sky9x/sdcard_driver.cpp sky9x/massstorage.cpp
   
   ifeq ($(SDCARD), YES)
-    SRC += FatFs/ff.c FatFs/fattime.c FatFs/option/ccsbcs.c sky9x/diskio.c
+    EXTRAINCDIRS += FatFs FatFs/option
+    EXTRABOARDSRC += FatFs/ff.c FatFs/fattime.c FatFs/option/ccsbcs.c sky9x/diskio.cpp
     CPPDEFS += -DVOICE
   endif
   
diff --git a/src/sky9x/audio.cpp b/src/sky9x/audio.cpp
index 9c3c3949b..ddc2500c2 100644
--- a/src/sky9x/audio.cpp
+++ b/src/sky9x/audio.cpp
@@ -34,7 +34,6 @@
 #include "../open9x.h"
 
 #if defined(SDCARD)
-
 const char * audioFilenames[] = {
   "inactiv",
   "lowbatt",
@@ -67,8 +66,6 @@ const char * audioFilenames[] = {
 
 uint32_t sdAvailableAudioFiles = 0;
 
-// TODO enable the assert when it's C++
-extern "C" {
 void retrieveAvailableAudioFiles()
 {
   FILINFO info;
@@ -80,10 +77,8 @@ void retrieveAvailableAudioFiles()
 
   char filename[32] = SYSTEM_SOUNDS_PATH "/";
 
-#if !defined WIN32 && defined __GNUC__
   assert(sizeof(audioFilenames)==AU_FRSKY_FIRST*sizeof(char *));
   assert(sizeof(sdAvailableAudioFiles)*8 > AU_FRSKY_FIRST);
-#endif
 
   uint32_t availableAudioFiles = 0;
 
@@ -96,7 +91,6 @@ void retrieveAvailableAudioFiles()
 
   sdAvailableAudioFiles = availableAudioFiles;
 }
-}
 
 inline bool isAudioFileAvailable(uint8_t i, char * filename)
 {
diff --git a/src/sky9x/diskio.c b/src/sky9x/diskio.cpp
similarity index 96%
rename from src/sky9x/diskio.c
rename to src/sky9x/diskio.cpp
index 429f9703f..c4bbb96ba 100644
--- a/src/sky9x/diskio.c
+++ b/src/sky9x/diskio.cpp
@@ -615,7 +615,6 @@ static const char * sdCmd52(uint8_t wrFlag,
   *status = HSMCI->HSMCI_RSPR[0];
   return 0;
 }
-#endif
 
 const char * sdSwReset(uint32_t retry)
 {
@@ -629,6 +628,7 @@ const char * sdSwReset(uint32_t retry)
     }
     return result;
 }
+#endif
 
 /**
  * \brief Run the SD/MMC/SDIO Mode initialization sequence.
@@ -954,8 +954,9 @@ void sdInit()
 #endif
 
 uint8_t sdErrorCount = 0;
-static FATFS g_FATFS_Obj = { 0 };
-void retrieveAvailableAudioFiles();
+FATFS g_FATFS_Obj = { 0 };
+
+extern void retrieveAvailableAudioFiles();
 
 void sdPoll10mS()
 {