diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_allocator.h b/compiler-rt/lib/sanitizer_common/sanitizer_allocator.h
index fde03adf3c25..24ffd1d08c44 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_allocator.h
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_allocator.h
@@ -354,7 +354,7 @@ class SizeClassAllocator32 {
     u32 offset = mem - beg;
     uptr n = offset / (u32)size;  // 32-bit division
     uptr meta = (beg + kRegionSize) - (n + 1) * kMetadataSize;
-    return (void*)meta;
+    return reinterpret_cast<void*>(meta);
   }
 
   bool PointerIsMine(void *p) {
@@ -365,6 +365,17 @@ class SizeClassAllocator32 {
     return possible_regions_[ComputeRegionId(reinterpret_cast<uptr>(p))] - 1;
   }
 
+  void *GetBlockBegin(void *p) {
+    CHECK(PointerIsMine(p));
+    uptr mem = reinterpret_cast<uptr>(p);
+    uptr beg = ComputeRegionBeg(mem);
+    uptr size = SizeClassMap::Size(GetSizeClass(p));
+    u32 offset = mem - beg;
+    u32 n = offset / (u32)size;  // 32-bit division
+    uptr res = beg + (n * (u32)size);
+    return reinterpret_cast<void*>(res);
+  }
+
   uptr GetActuallyAllocatedSize(void *p) {
     CHECK(PointerIsMine(p));
     return SizeClassMap::Size(GetSizeClass(p));
diff --git a/compiler-rt/lib/sanitizer_common/tests/sanitizer_allocator_test.cc b/compiler-rt/lib/sanitizer_common/tests/sanitizer_allocator_test.cc
index 684755bc9487..a01e08bc71c2 100644
--- a/compiler-rt/lib/sanitizer_common/tests/sanitizer_allocator_test.cc
+++ b/compiler-rt/lib/sanitizer_common/tests/sanitizer_allocator_test.cc
@@ -96,6 +96,8 @@ void TestSizeClassAllocator() {
       for (uptr i = 0; i < n_iter; i++) {
         void *x = a->Allocate(size, 1);
         allocated.push_back(x);
+        CHECK_EQ(x, a->GetBlockBegin(x));
+        CHECK_EQ(x, a->GetBlockBegin((char*)x + size - 1));
         CHECK(a->PointerIsMine(x));
         CHECK_GE(a->GetActuallyAllocatedSize(x), size);
         uptr class_id = a->GetSizeClass(x);