diff --git a/sys/compat/linprocfs/linprocfs_vnops.c b/sys/compat/linprocfs/linprocfs_vnops.c
index d506f650c57..ecec2d4b39b 100644
--- a/sys/compat/linprocfs/linprocfs_vnops.c
+++ b/sys/compat/linprocfs/linprocfs_vnops.c
@@ -54,6 +54,7 @@
 #include <sys/fcntl.h>
 #include <sys/proc.h>
 #include <sys/signalvar.h>
+#include <sys/sx.h>
 #include <sys/vnode.h>
 #include <sys/mount.h>
 #include <sys/namei.h>
diff --git a/sys/compat/svr4/svr4_misc.c b/sys/compat/svr4/svr4_misc.c
index 7d115f7d5e4..7e6ddd7a13e 100644
--- a/sys/compat/svr4/svr4_misc.c
+++ b/sys/compat/svr4/svr4_misc.c
@@ -52,6 +52,7 @@
 #include <sys/mount.h>
 #include <sys/resource.h>
 #include <sys/resourcevar.h>
+#include <sys/sx.h>
 #include <sys/vnode.h>
 #include <sys/uio.h>
 #include <sys/user.h>
diff --git a/sys/i386/ibcs2/ibcs2_sysvec.c b/sys/i386/ibcs2/ibcs2_sysvec.c
index 55b3a938deb..f2cbfcd3c06 100644
--- a/sys/i386/ibcs2/ibcs2_sysvec.c
+++ b/sys/i386/ibcs2/ibcs2_sysvec.c
@@ -37,6 +37,7 @@
 #include <sys/sysent.h>
 #include <sys/signalvar.h>
 #include <sys/proc.h>
+#include <sys/sx.h>
 
 #include <i386/ibcs2/ibcs2_syscall.h>
 #include <i386/ibcs2/ibcs2_signal.h>