Index: lib/Fuzzer/FuzzerInternal.h
===================================================================
--- lib/Fuzzer/FuzzerInternal.h
+++ lib/Fuzzer/FuzzerInternal.h
@@ -18,6 +18,7 @@
 #include <climits>
 #include <cstddef>
 #include <cstdlib>
+#include <pthread.h>
 #include <random>
 #include <string.h>
 #include <string>
@@ -125,7 +126,7 @@
 
 int NumberOfCpuCores();
 int GetPid();
-int SignalToMainThread();
+int SignalToMainThread(pthread_t MainThread);
 void SleepSeconds(int Seconds);
 
 class Random {
@@ -458,6 +459,10 @@
 
   // Maximum recorded coverage.
   Coverage MaxCoverage;
+
+  // Used to allow other threads to communicate with
+  // the thread the fuzzer was created in.
+  pthread_t MainThread;
 };
 
 }; // namespace fuzzer
Index: lib/Fuzzer/FuzzerLoop.cpp
===================================================================
--- lib/Fuzzer/FuzzerLoop.cpp
+++ lib/Fuzzer/FuzzerLoop.cpp
@@ -147,7 +147,7 @@
 };
 
 Fuzzer::Fuzzer(UserCallback CB, MutationDispatcher &MD, FuzzingOptions Options)
-    : CB(CB), MD(MD), Options(Options) {
+    : CB(CB), MD(MD), Options(Options), MainThread(pthread_self()) {
   SetDeathCallback();
   InitializeTraceState();
   assert(!F);
@@ -258,9 +258,11 @@
 
 void Fuzzer::RssLimitCallback() {
   InOOMState = true;
-  SignalToMainThread();
+  if (SignalToMainThread(MainThread)) {
+    Printf("WARNING: Failed to signal main thread.\n");
+  }
   SleepSeconds(5);
-  Printf("Signal to main thread failed (non-linux?). Exiting.\n");
+  Printf("ERROR: Should have exited already. Forcing exit.\n");
   _Exit(Options.ErrorExitCode);
   return;
 }
Index: lib/Fuzzer/FuzzerUtil.cpp
===================================================================
--- lib/Fuzzer/FuzzerUtil.cpp
+++ lib/Fuzzer/FuzzerUtil.cpp
@@ -248,12 +248,8 @@
 }
 
 int GetPid() { return getpid(); }
-int SignalToMainThread() {
-#ifdef __linux__
-  return syscall(SYS_tgkill, GetPid(), GetPid(), SIGALRM);
-#else
-  return 0;
-#endif
+int SignalToMainThread(pthread_t MainThread) {
+  return pthread_kill(MainThread, SIGALRM);
 }
 
 std::string Base64(const Unit &U) {