diff --git a/lib/libthr/Makefile b/lib/libthr/Makefile
--- a/lib/libthr/Makefile
+++ b/lib/libthr/Makefile
@@ -29,6 +29,12 @@
 CFLAGS.thr_stack.c+=	-Wno-cast-align
 CFLAGS.rtld_malloc.c+=	-Wno-cast-align
 CFLAGS.thr_symbols.c+=	-Wno-missing-variable-declarations
+.if ${MK_ASAN} != "no"
+# False-positive ASAN error claiming the local "struct sigaction act;" is
+# overflowed by handle_signal() reading from the ucontext_t argument. This
+# could be caused by ASAN not treating this function as a signal handler.
+CFLAGS.thr_sig.c+=	-fno-sanitize=address
+.endif
 
 .ifndef NO_THREAD_UNWIND_STACK
 CFLAGS+=-fexceptions