diff --git a/libraries/AP_HAL/AP_HAL_Main.h b/libraries/AP_HAL/AP_HAL_Main.h
index acc7815424..30bfd49618 100644
--- a/libraries/AP_HAL/AP_HAL_Main.h
+++ b/libraries/AP_HAL/AP_HAL_Main.h
@@ -18,6 +18,7 @@
 #if CONFIG_MAIN_WITHOUT_ARGC_ARGV
 
 #define AP_HAL_MAIN() extern "C" { \
+    int AP_MAIN(void); \
     int AP_MAIN(void) { \
         AP_HAL::HAL::FunCallbacks callbacks(setup, loop); \
         hal.run(0, NULL, &callbacks); \
@@ -26,6 +27,7 @@
     }
 
 #define AP_HAL_MAIN_CALLBACKS(CALLBACKS) extern "C" { \
+    int AP_MAIN(void); \
     int AP_MAIN(void) { \
         hal.run(0, NULL, CALLBACKS); \
         return 0; \
@@ -35,6 +37,7 @@
 #else
 
 #define AP_HAL_MAIN() extern "C" { \
+    int AP_MAIN(int argc, char* const argv[]); \
     int AP_MAIN(int argc, char* const argv[]) { \
         AP_HAL::HAL::FunCallbacks callbacks(setup, loop); \
         hal.run(argc, argv, &callbacks); \
@@ -43,6 +46,7 @@
     }
 
 #define AP_HAL_MAIN_CALLBACKS(CALLBACKS) extern "C" { \
+    int AP_MAIN(int argc, char* const argv[]); \
     int AP_MAIN(int argc, char* const argv[]) { \
         hal.run(argc, argv, CALLBACKS); \
         return 0; \