diff --git a/libraries/AP_HAL/AP_HAL_Namespace.h b/libraries/AP_HAL/AP_HAL_Namespace.h
index e224339f89..8452b3d37c 100644
--- a/libraries/AP_HAL/AP_HAL_Namespace.h
+++ b/libraries/AP_HAL/AP_HAL_Namespace.h
@@ -27,6 +27,14 @@
 #define DELEGATE_FUNCTION1(rettype, args...) fastdelegate::FastDelegate1<args, rettype>
 #define DELEGATE_FUNCTION2(rettype, args...) fastdelegate::FastDelegate2<args, rettype>
 
+#ifndef APM_BUILD_FUNCTOR
+#define APM_BUILD_FUNCTOR 0
+#endif
+
+#if APM_BUILD_FUNCTOR
+#include "utility/functor.h"
+#endif
+
 namespace AP_HAL {
 
     /* Toplevel pure virtual class Hal.*/
diff --git a/libraries/AP_Vehicle/AP_Vehicle.h b/libraries/AP_Vehicle/AP_Vehicle.h
index c6e8e2f348..f071463bca 100644
--- a/libraries/AP_Vehicle/AP_Vehicle.h
+++ b/libraries/AP_Vehicle/AP_Vehicle.h
@@ -74,6 +74,9 @@ public:
 #define APM_BUILD_TYPE(type) ((type) == APM_BUILD_UNKNOWN)
 #endif
 
+#ifndef APM_BUILD_FUNCTOR
+#define APM_BUILD_FUNCTOR 0
+#endif
 
 #if APM_BUILD_TYPE(APM_BUILD_APMrover2) || APM_BUILD_TYPE(APM_BUILD_ArduPlane)
 # define APM_BUILD_DELEGATES 1