Index: head/sys/arm/include/armreg.h
===================================================================
--- head/sys/arm/include/armreg.h
+++ head/sys/arm/include/armreg.h
@@ -41,6 +41,10 @@
 #ifndef MACHINE_ARMREG_H
 #define MACHINE_ARMREG_H
 
+#ifndef _SYS_CDEFS_H_
+#error Please include sys/cdefs.h before including machine/armreg.h
+#endif
+
 #define INSN_SIZE	4
 #define INSN_COND_MASK	0xf0000000	/* Condition mask */
 #define PSR_MODE        0x0000001f      /* mode mask */