diff --git a/lib/libc/amd64/string/Makefile.inc b/lib/libc/amd64/string/Makefile.inc
index b1369841bc74..d5bb646c5c53 100644
--- a/lib/libc/amd64/string/Makefile.inc
+++ b/lib/libc/amd64/string/Makefile.inc
@@ -1,30 +1,36 @@
 MDSRCS+= \
 	amd64_archlevel.c \
 	bcmp.S \
 	memchr.S \
 	memcmp.S \
 	memccpy.S \
 	memcpy.S \
 	memmove.S \
 	memrchr.S \
 	memset.S \
 	stpcpy.S \
 	stpncpy.S \
 	strcat.S \
 	strchrnul.S \
 	strcmp.S \
 	strcpy.c \
 	strcspn.S \
 	strlcat.c \
 	strlcpy.S \
 	strlen.S \
 	strncat.c \
 	strncmp.S \
 	strncpy.c \
 	strnlen.c \
 	strpbrk.c \
 	strrchr.S \
 	strsep.c \
 	strspn.S \
 	timingsafe_bcmp.S \
 	timingsafe_memcmp.S
+
+.if ${MK_ASAN} != "no"
+# Disable ASAN for amd64_archlevel.c since its code is executed before the
+# sanitizer runtime can initialize itself.
+CFLAGS.amd64_archlevel.c+=	-fno-sanitize=address
+.endif