Index: lib/fuzzer/FuzzerExtFunctionsDlsym.cpp
===================================================================
--- lib/fuzzer/FuzzerExtFunctionsDlsym.cpp
+++ lib/fuzzer/FuzzerExtFunctionsDlsym.cpp
@@ -12,7 +12,7 @@
 // That is a complication we don't wish to expose to clients right now.
 //===----------------------------------------------------------------------===//
 #include "FuzzerDefs.h"
-#if LIBFUZZER_APPLE
+#if LIBFUZZER_APPLE && !UNDEFINED_WEAK_SYMBOLS_ALLOWED
 
 #include "FuzzerExtFunctions.h"
 #include "FuzzerIO.h"
Index: lib/fuzzer/FuzzerExtFunctionsWeak.cpp
===================================================================
--- lib/fuzzer/FuzzerExtFunctionsWeak.cpp
+++ lib/fuzzer/FuzzerExtFunctionsWeak.cpp
@@ -10,10 +10,11 @@
 // symbols. We don't use this approach on Apple platforms because it requires
 // clients of LibFuzzer to pass ``-U _<symbol_name>`` to the linker to allow
 // weak symbols to be undefined. That is a complication we don't want to expose
-// to clients right now.
+// to clients right now. However, if someone prefers that way, they need to
+// define UNDEFINED_WEAK_SYMBOLS_ALLOWED explicitly.
 //===----------------------------------------------------------------------===//
 #include "FuzzerDefs.h"
-#if LIBFUZZER_LINUX || LIBFUZZER_NETBSD
+#if LIBFUZZER_LINUX || LIBFUZZER_NETBSD || UNDEFINED_WEAK_SYMBOLS_ALLOWED
 
 #include "FuzzerExtFunctions.h"
 #include "FuzzerIO.h"