Index: lib/asan/asan_poisoning.cc
===================================================================
--- lib/asan/asan_poisoning.cc
+++ lib/asan/asan_poisoning.cc
@@ -412,10 +412,10 @@
   // ending with end.
   uptr kMaxRangeToCheck = 32;
   uptr r1_beg = beg;
-  uptr r1_end = Min(end + kMaxRangeToCheck, mid);
-  uptr r2_beg = Max(beg, mid - kMaxRangeToCheck);
-  uptr r2_end = Min(end, mid + kMaxRangeToCheck);
-  uptr r3_beg = Max(end - kMaxRangeToCheck, mid);
+  uptr r1_end = Min(beg + kMaxRangeToCheck, mid);
+  uptr r2_beg = Max(r1_end, mid - kMaxRangeToCheck/2);
+  uptr r2_end = Min(end, mid + kMaxRangeToCheck/2);
+  uptr r3_beg = Max(r2_end, end - kMaxRangeToCheck);
   uptr r3_end = end;
   for (uptr i = r1_beg; i < r1_end; i++)
     if (AddressIsPoisoned(i))