diff --git a/sys/modules/linprocfs/Makefile b/sys/modules/linprocfs/Makefile
index 6408a9882147..fa7ac8725d14 100644
--- a/sys/modules/linprocfs/Makefile
+++ b/sys/modules/linprocfs/Makefile
@@ -7,4 +7,8 @@ SRCS=	vnode_if.h \
 	device_if.h bus_if.h \
 	linprocfs.c
 
+.if !defined(KERNBUILDDIR)
+.warning Building Linuxulator outside of a kernel does not make sense
+.endif
+
 .include <bsd.kmod.mk>
diff --git a/sys/modules/linsysfs/Makefile b/sys/modules/linsysfs/Makefile
index 6eaa844e9ea5..058fbbc521b1 100644
--- a/sys/modules/linsysfs/Makefile
+++ b/sys/modules/linsysfs/Makefile
@@ -7,4 +7,8 @@ SRCS=	vnode_if.h \
 	device_if.h bus_if.h  pci_if.h \
 	linsysfs.c
 
+.if !defined(KERNBUILDDIR)
+.warning Building Linuxulator outside of a kernel does not make sense
+.endif
+
 .include <bsd.kmod.mk>
diff --git a/sys/modules/linux/Makefile b/sys/modules/linux/Makefile
index fff940db5de0..e2d6d6056c44 100644
--- a/sys/modules/linux/Makefile
+++ b/sys/modules/linux/Makefile
@@ -80,4 +80,8 @@ ${VDSO}.so: linux${SFX}_locore.o
 linux${SFX}_genassym.o: offset.inc
 	${CC} -c ${CFLAGS:N-flto:N-fno-common} ${.IMPSRC}
 
+.if !defined(KERNBUILDDIR)
+.warning Building Linuxulator outside of a kernel does not make sense
+.endif
+
 .include <bsd.kmod.mk>
diff --git a/sys/modules/linux64/Makefile b/sys/modules/linux64/Makefile
index 8d4bbfa64f4f..1f6250dcd2e6 100644
--- a/sys/modules/linux64/Makefile
+++ b/sys/modules/linux64/Makefile
@@ -55,4 +55,8 @@ linux_support.o: assym.inc linux_assym.h
 linux_genassym.o: offset.inc
 	${CC} -c ${CFLAGS:N-flto:N-fno-common} ${.IMPSRC}
 
+.if !defined(KERNBUILDDIR)
+.warning Building Linuxulator outside of a kernel does not make sense
+.endif
+
 .include <bsd.kmod.mk>
diff --git a/sys/modules/linux_common/Makefile b/sys/modules/linux_common/Makefile
index 9fb0210810fb..5b49a7409997 100644
--- a/sys/modules/linux_common/Makefile
+++ b/sys/modules/linux_common/Makefile
@@ -15,4 +15,8 @@ EXPORT_SYMS+=	linux_ioctl_unregister_handler
 EXPORT_SYMS+=	linux_get_osname
 EXPORT_SYMS+=	linux_get_osrelease
 
+.if !defined(KERNBUILDDIR)
+.warning Building Linuxulator outside of a kernel does not make sense
+.endif
+
 .include <bsd.kmod.mk>