Index: sys/modules/linprocfs/Makefile
===================================================================
--- sys/modules/linprocfs/Makefile
+++ sys/modules/linprocfs/Makefile
@@ -7,4 +7,8 @@
 	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>
Index: sys/modules/linsysfs/Makefile
===================================================================
--- sys/modules/linsysfs/Makefile
+++ sys/modules/linsysfs/Makefile
@@ -7,4 +7,8 @@
 	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>
Index: sys/modules/linux/Makefile
===================================================================
--- sys/modules/linux/Makefile
+++ sys/modules/linux/Makefile
@@ -81,12 +81,7 @@
 	${CC} -c ${CFLAGS:N-flto:N-fno-common} ${.IMPSRC}
 
 .if !defined(KERNBUILDDIR)
-.if defined(KTR)
-CFLAGS+=	-DKTR
-.endif
-.if defined(DEBUG)
-CFLAGS+=	-DDEBUG
-.endif
+.warning Building Linuxulator outside of a kernel does not make sense
 .endif
 
 .include <bsd.kmod.mk>
Index: sys/modules/linux64/Makefile
===================================================================
--- sys/modules/linux64/Makefile
+++ sys/modules/linux64/Makefile
@@ -56,12 +56,7 @@
 	${CC} -c ${CFLAGS:N-flto:N-fno-common} ${.IMPSRC}
 
 .if !defined(KERNBUILDDIR)
-.if defined(DEBUG)
-CFLAGS+=-DDEBUG
-.endif
-.if defined(KTR)
-CFLAGS+=-DKTR
-.endif
+.warning Building Linuxulator outside of a kernel does not make sense
 .endif
 
 .include <bsd.kmod.mk>
Index: sys/modules/linux_common/Makefile
===================================================================
--- sys/modules/linux_common/Makefile
+++ sys/modules/linux_common/Makefile
@@ -16,12 +16,7 @@
 EXPORT_SYMS+=	linux_get_osrelease
 
 .if !defined(KERNBUILDDIR)
-.if defined(DEBUG)
-CFLAGS+=-DDEBUG
-.endif
-.if defined(KTR)
-CFLAGS+=-DKTR
-.endif
+.warning Building Linuxulator outside of a kernel does not make sense
 .endif
 
 .include <bsd.kmod.mk>