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diff --git a/immer/heap/debug_size_heap.hpp b/immer/heap/debug_size_heap.hpp
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+++ b/immer/heap/debug_size_heap.hpp
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+//
+// immer: immutable data structures for C++
+// Copyright (C) 2016, 2017, 2018 Juan Pedro Bolivar Puente
+//
+// This software is distributed under the Boost Software License, Version 1.0.
+// See accompanying file LICENSE or copy at http://boost.org/LICENSE_1_0.txt
+//
+
+#pragma once
+
+#include <immer/config.hpp>
+#include <immer/heap/identity_heap.hpp>
+
+#include <cassert>
+#include <cstddef>
+#include <type_traits>
+#include <memory>
+
+namespace immer {
+
+#if IMMER_ENABLE_DEBUG_SIZE_HEAP
+
+/*!
+ * A heap that in debug mode ensures that the sizes for allocation and
+ * deallocation do match.
+ */
+template <typename Base>
+struct debug_size_heap
+{
+#if defined(__MINGW32__) && !defined(__MINGW64__)
+    // There is a bug in MinGW 32bit:
+    // https://sourceforge.net/p/mingw-w64/bugs/778/ It causes different
+    // versions of std::max_align_t to be defined, depending on inclusion order
+    // of stddef.h and stdint.h. As we have no control over the inclusion order
+    // here (as it might be set in stone by the outside world), we can't easily
+    // pin it to one of both versions of std::max_align_t. This means, we have
+    // to hardcode extra_size for MinGW 32bit builds until the mentioned bug is
+    // fixed.
+    constexpr static auto extra_size = 8;
+#else
+    constexpr static auto extra_size = sizeof(
+        std::aligned_storage_t<sizeof(std::size_t), alignof(std::max_align_t)>);
+#endif
+
+    template <typename... Tags>
+    static void* allocate(std::size_t size, Tags... tags)
+    {
+        auto p = (std::size_t*) Base::allocate(size + extra_size, tags...);
+        new (p) std::size_t{size};
+        return ((char*) p) + extra_size;
+    }
+
+    template <typename... Tags>
+    static void deallocate(std::size_t size, void* data, Tags... tags)
+    {
+        auto p = (std::size_t*) (((char*) data) - extra_size);
+        assert(*p == size);
+        Base::deallocate(size + extra_size, p, tags...);
+    }
+};
+
+#else // IMMER_ENABLE_DEBUG_SIZE_HEAP
+
+template <typename Base>
+using debug_size_heap = identity_heap<Base>;
+
+#endif // !IMMER_ENABLE_DEBUG_SIZE_HEAP
+
+} // namespace immer