diff -r 05bc673089da sys/conf/Makefile.kern.inc
--- sys/conf/Makefile.kern.inc	Fri Dec 31 14:41:48 2021 +0100
+++ sys/conf/Makefile.kern.inc	Fri Dec 31 15:24:05 2021 +0100
@@ -267,7 +267,7 @@ TARGETSFX=	.gdb
 LINKFLAGS+=	${LINKFLAGS_NORMAL}
 .endif
 
-.if ${MKDEBUG:Uno} == "yes"
+.if ${MKDEBUG:Uno} == "yes" && ${_SRC_TOP_} != ""
 # XXX: KERNEL_DIR?
 debuginstall: install-kernel-debug
 .for k in ${KERNELS}