diff --git a/libraries/AP_Common/AP_Common.h b/libraries/AP_Common/AP_Common.h
index b50ab3d2a4..3134ac12ab 100644
--- a/libraries/AP_Common/AP_Common.h
+++ b/libraries/AP_Common/AP_Common.h
@@ -24,6 +24,9 @@
 #pragma GCC diagnostic warning "-Wlogical-op"
 #pragma GCC diagnostic ignored "-Wredundant-decls"
 
+// used to pack structures
+#define PACKED __attribute__((__packed__))
+
 // Make some dire warnings into errors
 //
 // Some warnings indicate questionable code; rather than let