diff --git a/libraries/AP_Filesystem/AP_Filesystem_FATFS.cpp b/libraries/AP_Filesystem/AP_Filesystem_FATFS.cpp
index 58b387b553..f728b3362c 100644
--- a/libraries/AP_Filesystem/AP_Filesystem_FATFS.cpp
+++ b/libraries/AP_Filesystem/AP_Filesystem_FATFS.cpp
@@ -9,7 +9,7 @@
 #include <AP_HAL/AP_HAL.h>
 #include <AP_Math/AP_Math.h>
 #include <stdio.h>
-#include <AP_RTC/AP_RTC.h>
+#include <AP_Common/time.h>
 
 #include <ff.h>
 #include <AP_HAL_ChibiOS/sdcard.h>
@@ -564,7 +564,7 @@ static time_t fat_time_to_unix(uint16_t date, uint16_t time)
     tp.tm_mday = (date & 0x1f);
     tp.tm_mon = ((date >> 5) & 0x0f) - 1;
     tp.tm_year = ((date >> 9) & 0x7f) + 80;
-    unix = AP::rtc().mktime(&tp);
+    unix = ap_mktime(&tp);
     return unix;
 }