diff --git a/libraries/AP_HAL/board/linux.h b/libraries/AP_HAL/board/linux.h
index 53822de9b2..a26cb8d1c5 100644
--- a/libraries/AP_HAL/board/linux.h
+++ b/libraries/AP_HAL/board/linux.h
@@ -341,6 +341,10 @@
     #error "no Linux board subtype set"
 #endif
 
+#ifndef BOARD_FLASH_SIZE
+#define BOARD_FLASH_SIZE 4096
+#endif
+
 #ifndef HAL_OPTFLOW_PX4FLOW_I2C_ADDRESS
     #define HAL_OPTFLOW_PX4FLOW_I2C_ADDRESS 0x42
 #endif
diff --git a/libraries/AP_HAL/board/sitl.h b/libraries/AP_HAL/board/sitl.h
index 2710a78ff4..7738814898 100644
--- a/libraries/AP_HAL/board/sitl.h
+++ b/libraries/AP_HAL/board/sitl.h
@@ -29,6 +29,10 @@
 #define HAL_FLASH_ALLOW_UPDATE 0
 #endif
 
+#ifndef BOARD_FLASH_SIZE
+#define BOARD_FLASH_SIZE 4096
+#endif
+
 #ifndef HAL_STORAGE_SIZE
 #define HAL_STORAGE_SIZE            32768
 #endif