Index: sys/conf/kmod.mk
===================================================================
--- sys/conf/kmod.mk
+++ sys/conf/kmod.mk
@@ -91,7 +91,9 @@
 WERROR?=	-Werror
 CFLAGS+=	${WERROR}
 CFLAGS+=	-D_KERNEL
+.if !defined(KERNBUILDDIR)
 CFLAGS+=	-DKLD_MODULE
+.endif
 
 # Don't use any standard or source-relative include directories.
 NOSTDINC=	-nostdinc