diff --git a/compiler-rt/lib/asan/asan_mac.cpp b/compiler-rt/lib/asan/asan_mac.cpp
--- a/compiler-rt/lib/asan/asan_mac.cpp
+++ b/compiler-rt/lib/asan/asan_mac.cpp
@@ -55,7 +55,8 @@
 }
 
 uptr FindDynamicShadowStart() {
-  return MapDynamicShadow(MemToShadowSize(kHighMemEnd), SHADOW_SCALE,
+  // VM range is [0, kHighMemEnd] so size is (kHighMemEnd - 0 + 1).
+  return MapDynamicShadow(MemToShadowSize(kHighMemEnd + 1), SHADOW_SCALE,
                           /*min_shadow_base_alignment*/ 0, kHighMemEnd);
 }