diff --git a/compiler-rt/lib/tsan/rtl/tsan_rtl.cpp b/compiler-rt/lib/tsan/rtl/tsan_rtl.cpp
--- a/compiler-rt/lib/tsan/rtl/tsan_rtl.cpp
+++ b/compiler-rt/lib/tsan/rtl/tsan_rtl.cpp
@@ -132,6 +132,10 @@
   ctx->trace_part_finished_excess = 0;
 }
 
+uptr mapped_shadow_begin;
+uptr mapped_shadow_end;
+bool mapped_shadow_captured;
+
 static void DoResetImpl(uptr epoch) {
   ThreadRegistryLock lock0(&ctx->thread_registry);
   Lock lock1(&ctx->slot_mtx);
@@ -197,8 +201,13 @@
   }
 
   DPrintf("Resetting shadow...\n");
-  if (!MmapFixedSuperNoReserve(ShadowBeg(), ShadowEnd() - ShadowBeg(),
-                               "shadow")) {
+  auto shadow_begin = ShadowBeg();
+  auto shadow_end = ShadowEnd();
+  if (mapped_shadow_captured) {
+    shadow_begin = mapped_shadow_begin;
+    shadow_end = mapped_shadow_end;
+  }
+  if (!MmapFixedSuperNoReserve(shadow_begin, shadow_end - shadow_begin, "shadow")) {
     Printf("failed to reset shadow memory\n");
     Die();
   }
@@ -563,9 +572,10 @@
   // so we can get away with unaligned mapping.
   // CHECK_EQ(addr, addr & ~((64 << 10) - 1));  // windows wants 64K alignment
   const uptr kPageSize = GetPageSizeCached();
-  uptr shadow_begin = RoundDownTo((uptr)MemToShadow(addr), kPageSize);
-  uptr shadow_end = RoundUpTo((uptr)MemToShadow(addr + size), kPageSize);
-  if (!MmapFixedSuperNoReserve(shadow_begin, shadow_end - shadow_begin,
+  mapped_shadow_begin = RoundDownTo((uptr)MemToShadow(addr), kPageSize);
+  mapped_shadow_end = RoundUpTo((uptr)MemToShadow(addr + size), kPageSize);
+  mapped_shadow_captured = true;
+  if (!MmapFixedSuperNoReserve(mapped_shadow_begin, mapped_shadow_end - mapped_shadow_begin,
                                "shadow"))
     Die();