diff --git a/compiler-rt/lib/scudo/standalone/primary32.h b/compiler-rt/lib/scudo/standalone/primary32.h
--- a/compiler-rt/lib/scudo/standalone/primary32.h
+++ b/compiler-rt/lib/scudo/standalone/primary32.h
@@ -708,8 +708,10 @@
       if (AllocatedGroupSize == 0)
         continue;
 
+      // TransferBatches are pushed in fromt of BG.Batches. The first one may
+      // not have all caches used.
       const uptr NumBlocks = (BG.Batches.size() - 1) * BG.MaxCachedPerBatch +
-                             BG.Batches.back()->getCount();
+                             BG.Batches.front()->getCount();
       const uptr BytesInBG = NumBlocks * BlockSize;
       // Given the randomness property, we try to release the pages only if the
       // bytes used by free blocks exceed certain proportion of allocated
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
@@ -702,16 +702,22 @@
           BG.PushedBlocks - BG.PushedBlocksAtLastCheckpoint;
       if (PushedBytesDelta * BlockSize < PageSize)
         continue;
-      const uptr BatchGroupEnd =
-          batchGroupBase(BG.GroupId, CompactPtrBase) + GroupSize;
-      const uptr AllocatedGroupSize = AllocatedUserEnd >= BatchGroupEnd
-                                          ? GroupSize
-                                          : AllocatedUserEnd - BatchGroupEnd;
+      // Group boundary is not necessary to have same alignment as Region. It
+      // may sit across Region boundary.
+      const uptr BatchGroupBeg =
+          Max(batchGroupBase(BG.GroupId, CompactPtrBase), Region->RegionBeg);
+      DCHECK_GE(AllocatedUserEnd, BatchGroupBeg);
+      const uptr AllocatedGroupSize =
+          AllocatedUserEnd >= BatchGroupBeg + GroupSize
+              ? GroupSize
+              : AllocatedUserEnd - BatchGroupBeg;
       if (AllocatedGroupSize == 0)
         continue;
 
+      // TransferBatches are pushed in fromt of BG.Batches. The first one may
+      // not have all caches used.
       const uptr NumBlocks = (BG.Batches.size() - 1) * BG.MaxCachedPerBatch +
-                             BG.Batches.back()->getCount();
+                             BG.Batches.front()->getCount();
       const uptr BytesInBG = NumBlocks * BlockSize;
       // Given the randomness property, we try to release the pages only if the
       // bytes used by free blocks exceed certain proportion of group size. Note