diff --git a/sys/kern/kern_mib.c b/sys/kern/kern_mib.c
index b739a17ddd9..7ec4aea9832 100644
--- a/sys/kern/kern_mib.c
+++ b/sys/kern/kern_mib.c
@@ -112,6 +112,7 @@ SYSCTL_INT(_kern, OID_AUTO, maxusers, CTLFLAG_RD,
 SYSCTL_INT(_kern, KERN_ARGMAX, argmax, CTLFLAG_RD,
     0, ARG_MAX, "Maximum bytes of argument to execve(2)");
 
+#include <sys/_posix.h>
 SYSCTL_INT(_kern, KERN_POSIX1, posix1version, CTLFLAG_RD,
     0, _KPOSIX_VERSION, "Version of POSIX attempting to comply to");