Index: lib/tsan/rtl/tsan_interceptors.cc
===================================================================
--- lib/tsan/rtl/tsan_interceptors.cc
+++ lib/tsan/rtl/tsan_interceptors.cc
@@ -663,8 +663,11 @@
 }
 
 TSAN_INTERCEPTOR(void*, memset, void *dst, int v, uptr size) {
-  SCOPED_TSAN_INTERCEPTOR(memset, dst, v, size);
-  MemoryAccessRange(thr, pc, (uptr)dst, size, true);
+  // On FreeBSD we get here from libthr internals on thread initialization.
+  if (cur_thread()->is_inited) {
+    SCOPED_TSAN_INTERCEPTOR(memset, dst, v, size);
+    MemoryAccessRange(thr, pc, (uptr)dst, size, true);
+  }
   return internal_memset(dst, v, size);
 }
 
@@ -2318,6 +2321,9 @@
   HandleRecvmsg(((TsanInterceptorContext *)ctx)->thr, \
       ((TsanInterceptorContext *)ctx)->pc, msg)
 
+#define COMMON_INTERCEPTOR_NOTHING_IS_INITIALIZED \
+  (!cur_thread()->is_inited)
+
 #include "sanitizer_common/sanitizer_common_interceptors.inc"
 
 #define TSAN_SYSCALL() \