Index: sys/arm/arm/machdep.c
===================================================================
--- sys/arm/arm/machdep.c
+++ sys/arm/arm/machdep.c
@@ -178,6 +178,12 @@
 #define	debugf(fmt, args...)
 #endif
 
+#if defined(COMPAT_FREEBSD4) || defined(COMPAT_FREEBSD5) || \
+    defined(COMPAT_FREEBSD6) || defined(COMPAT_FREEBSD7) || \
+    defined(COMPAT_FREEBSD9)
+#error FreeBSD/arm doesn't provide compatibility with releases prior to 10
+#endif
+
 struct pcpu __pcpu[MAXCPU];
 struct pcpu *pcpup = &__pcpu[0];