diff --git a/libraries/Desktop/support/DataFlash_APM1.cpp b/libraries/Desktop/support/DataFlash_APM1.cpp
index b45d9d3128..1fb7b5a608 100644
--- a/libraries/Desktop/support/DataFlash_APM1.cpp
+++ b/libraries/Desktop/support/DataFlash_APM1.cpp
@@ -10,6 +10,7 @@
 #include <stdint.h>
 #include "DataFlash.h"
 #include <SPI.h>
+#include <AP_Semaphore.h>
 
 #define DF_PAGE_SIZE 512
 #define DF_NUM_PAGES 4096