diff --git a/experimental/extrinsic_storage.h b/experimental/extrinsic_storage.h
index a1d1822772..719b98ea92 100644
--- a/experimental/extrinsic_storage.h
+++ b/experimental/extrinsic_storage.h
@@ -8,25 +8,21 @@
 #ifndef CPP2_EXPERIMENTAL_EXTRINSIC_STORAGE_H
 #define CPP2_EXPERIMENTAL_EXTRINSIC_STORAGE_H
 
-
 //  *****************************************************************
 //  Enable/disable debug instrumentation and statistics printing here
-constexpr auto debug_instrumentation = true;
+constexpr inline auto debug_instrumentation = false;
 //  *****************************************************************
 
-
 #include <algorithm>
 #include <array>
 #include <atomic>
 #include <cassert>
 #include <cstdint>
-#include <fstream>
 #include <functional>
+#include <iostream>
 #include <memory>
 #include <map>
-#include <iostream>
 #include <ranges>
-#include <source_location>
 #include <string>
 #include <type_traits>
 
diff --git a/experimental/extrinsic_storage_std_locked.h b/experimental/extrinsic_storage_std_locked.h
new file mode 100644
index 0000000000..bfbea55336
--- /dev/null
+++ b/experimental/extrinsic_storage_std_locked.h
@@ -0,0 +1,76 @@
+
+//  Copyright 2022-2024 Herb Sutter
+//  SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//  
+//  Part of the Cppfront Project, under the Apache License v2.0 with LLVM Exceptions.
+//  See https://github.com/hsutter/cppfront/blob/main/LICENSE for license information.
+
+#ifndef CPP2_EXPERIMENTAL_EXTRINSIC_STORAGE_STD_LOCKED_H
+#define CPP2_EXPERIMENTAL_EXTRINSIC_STORAGE_STD_LOCKED_H
+
+#include <map>
+#include <mutex>
+#include <string>
+#include <unordered_map>
+
+
+//-----------------------------------------------------------------------------------
+//  Some helpers
+//
+auto print(std::integral auto val) -> std::string {
+    auto ret = std::to_string(val % 10);
+    auto pos = 0;
+    while ((val /= 10) > 0) {
+        if ((++pos % 3) == 0) { ret = ',' + ret; }
+        ret = std::to_string(val % 10) + ret;
+    }
+    return ret;
+}
+
+
+//-----------------------------------------------------------------------------------
+//  A "brute-force" locked implementation to measure against
+//
+//  NOTE: For performance comparison only, not recommended
+//
+template <typename Data>
+class extrinsic_storage {
+    std::mutex                     mut;
+    //std::map<void*,Data>           data;
+    std::unordered_map<void*,Data> data;
+public:
+    //--------------------------------------------------------------------------
+    //  find_or_insert( pobj ) - returns the data entry for pobj
+    //
+    //  If pobj does not yet have an entry, creates it
+    //
+    auto find_or_insert(void* pobj) -> Data* {
+        auto _ = std::lock_guard{mut};
+        return &data[pobj];
+    }
+
+    //--------------------------------------------------------------------------
+    //  find( pobj ) - returns the data entry for pobj or null if not present
+    //
+    auto find(void* pobj) noexcept -> Data* {
+        auto _ = std::lock_guard{mut};
+        if (auto iter = data.find(pobj);
+            iter != data.end()
+            )
+        {
+            return &iter->second;
+        }
+        // Else
+        return nullptr;
+    }
+
+    //--------------------------------------------------------------------------
+    //  erase( pobj ) - removes the entry for pobj
+    //
+    auto erase(void* pobj) noexcept -> void {
+        auto _ = std::lock_guard{mut};
+        data.erase(pobj);
+    }
+};
+
+#endif
diff --git a/experimental/union_test.cpp b/experimental/union_test.cpp
index 77d5365a9d..33e2fff1f3 100644
--- a/experimental/union_test.cpp
+++ b/experimental/union_test.cpp
@@ -5,10 +5,14 @@
 //  Part of the Cppfront Project, under the Apache License v2.0 with LLVM Exceptions.
 //  See https://github.com/hsutter/cppfront/blob/main/LICENSE for license information.
 
+//#include "extrinsic_storage_std_locked.h"
 #include "extrinsic_storage.h"
 
 #include <chrono>
 #include <cstdint>
+#include <fstream>
+#include <iostream>
+#include <source_location>
 #include <thread>
 #include <vector>