diff --git a/compiler-rt/lib/scudo/standalone/primary64.h b/compiler-rt/lib/scudo/standalone/primary64.h
--- a/compiler-rt/lib/scudo/standalone/primary64.h
+++ b/compiler-rt/lib/scudo/standalone/primary64.h
@@ -756,14 +756,8 @@
       }
       // TODO: Consider allocating MemMap in init().
       if (!Region->MemMap.isAllocated()) {
-        // TODO: Ideally, a region should reserve RegionSize because the memory
-        // between `RegionBeg` and region base is still belong to a region and
-        // it's just not used. In order to make it work on every platform (some
-        // of them don't support `remap()` across the unused range), dispatch
-        // from `RegionBeg` for now.
-        const uptr ReserveSize =
-            RegionSize - (RegionBeg - getRegionBaseByClassId(ClassId));
-        Region->MemMap = ReservedMemory.dispatch(RegionBeg, ReserveSize);
+        Region->MemMap = ReservedMemory.dispatch(
+            getRegionBaseByClassId(ClassId), RegionSize);
       }
       DCHECK(Region->MemMap.isAllocated());