Index: sysutils/openzfs-kmod/Makefile
===================================================================
--- sysutils/openzfs-kmod/Makefile
+++ sysutils/openzfs-kmod/Makefile
@@ -32,6 +32,11 @@
 IGNORE=	needs FreeBSD 12/13 with AES-CCM support
 .endif
 
+.if !exists(${SRC_BASE}/sys/Makefile)
+IGNORE= requires kernel source files in ${SRC_BASE}
+.endif
+MAKE_OPTS+=	SYSDIR=${SRC_BASE}/sys
+
 .if ${PORT_OPTIONS:MDEBUG}
 MAKE_OPTS+=	WITH_DEBUG=true
 PLIST_FILES+=	${KMODDIR}/${KMODTARGET}.debug