diff --git a/compiler-rt/test/ubsan/TestCases/Misc/monitor.cpp b/compiler-rt/test/ubsan/TestCases/Misc/monitor.cpp
--- a/compiler-rt/test/ubsan/TestCases/Misc/monitor.cpp
+++ b/compiler-rt/test/ubsan/TestCases/Misc/monitor.cpp
@@ -8,6 +8,21 @@
 // Linkage issue
 // XFAIL: openbsd
 
+// Apple's dynamic linker won't weak-def_coalesce in this file unless there is
+// at least one weak symbol and so this local __ubsan_on_report never has the
+// chance to be linked in even though it may be seen first. The behavior of weak
+// defined symbols in the context of dynamic linking is undefined and so this
+// behavior does not violate any "rules" per-se. Obviously there are other
+// platforms (above) that are having issues with the "strong-wins-over-weak"
+// expectation but while it works that way when static linked, not so in all
+// cases when dynamically linked. The weak symbol that gets the dynamic linker
+// to consider this compilation unit doesn't even have to be __ubsan_on_report
+// so the workaround until we move to a better pattern for registering what
+// amounts to a callback, is just to add *any* weak symbol to the comp unit.
+#if defined(__APPLE__)
+int __attribute((weak)) foo;
+#endif
+
 #include <cstdio>
 
 extern "C" {