diff --git a/sys/sys/_types.h b/sys/sys/_types.h
--- a/sys/sys/_types.h
+++ b/sys/sys/_types.h
@@ -161,7 +161,10 @@
 typedef int		__cpusetid_t;	/* cpuset identifier. */
 typedef __int64_t	__daddr_t;	/* bwrite(3), FIOBMAP2, etc */
 
-#if !defined(__has_feature) || !__has_feature(capabilities)
+#ifndef __has_feature
+#define __has_feature(x)        0
+#endif
+#if !__has_feature(capabilities)
 /*
  * On non-CHERI systems, define __(u)intcap_t to __(u)intptr_t so that
  * hybrid-C code which needs to be explicitly aware of capabilities can