diff --git a/stand/defs.mk b/stand/defs.mk
--- a/stand/defs.mk
+++ b/stand/defs.mk
@@ -24,6 +24,12 @@
 # enough to make that hassle worth chasing.
 _CPUCFLAGS=
 
+.if ${LDFLAGS:M-nostdlib}
+# Sanitizers won't work unless we link against libc (e.g. in userboot/test).
+MK_ASAN:=	no
+MK_UBSAN:=	no
+.endif
+
 .include <src.opts.mk>
 .include <bsd.linker.mk>
 
diff --git a/stand/userboot/userboot/Makefile b/stand/userboot/userboot/Makefile
--- a/stand/userboot/userboot/Makefile
+++ b/stand/userboot/userboot/Makefile
@@ -6,6 +6,9 @@
 LOADER_EXT2FS_SUPPORT?=	no
 PIC=yes
 
+# Note: -nostdlib needs to be added to LDFLAGS before including defs.mk
+LDFLAGS+=	-nostdlib -Wl,-Bsymbolic
+
 .include <bsd.init.mk>
 
 SHLIB_NAME=	userboot_${LOADER_INTERP}.so
@@ -39,8 +42,6 @@
 CFLAGS.gfx_fb.c+= -I$(SRCTOP)/sys/teken -I${SRCTOP}/contrib/pnglite
 CWARNFLAGS.main.c += -Wno-implicit-function-declaration
 
-LDFLAGS+=	-nostdlib -Wl,-Bsymbolic
-
 NEWVERSWHAT=	"User boot ${LOADER_INTERP}" ${MACHINE_CPUARCH}
 VERSION_FILE=	${.CURDIR}/../userboot/version