diff --git a/include/realtime_memory/memory_resources.h b/include/realtime_memory/memory_resources.h
index 854e2a0..ecf31e4 100644
--- a/include/realtime_memory/memory_resources.h
+++ b/include/realtime_memory/memory_resources.h
@@ -4,8 +4,6 @@
 #pragma once
 #include "pmr_includes.h"
 
-PMR_DIAGNOSTIC_PUSH
-
 //==============================================================================
 namespace cradle::pmr
 {
@@ -626,5 +624,3 @@ inline bool unsynchronized_pool_resource::is_oversized (std::size_t bytes, std::
 }
 
 } // namespace cradle::pmr
-
-PMR_DIAGNOSTIC_POP
diff --git a/include/realtime_memory/pmr_includes.h b/include/realtime_memory/pmr_includes.h
index cdcf4db..cac3184 100644
--- a/include/realtime_memory/pmr_includes.h
+++ b/include/realtime_memory/pmr_includes.h
@@ -6,28 +6,17 @@
 #include <vector>
 
 #if defined (__apple_build_version__)
- #define USE_EXPERIMENTAL_PMR __apple_build_version__ < 15000000 || __MAC_OS_X_VERSION_MIN_REQUIRED < 140000
+ #define USE_PMR_SHIM 1
 #elif defined (__clang__)
- #define USE_EXPERIMENTAL_PMR _LIBCPP_VERSION < 1600
+ #define USE_PMR_SHIM _LIBCPP_VERSION < 1600
 #else
- #define USE_EXPERIMENTAL_PMR 0
+ #define USE_PMR_SHIM 0
 #endif
 
-#if USE_EXPERIMENTAL_PMR
- #include <experimental/memory_resource>
- namespace std_pmr = std::experimental::pmr;
+#if USE_PMR_SHIM
+ #include "pmr_shim.h"
+ namespace std_pmr = rtm_pmr;
 #else
  #include <memory_resource>
  namespace std_pmr = std::pmr;
 #endif
-
-#if defined (__apple_build_version__) && USE_EXPERIMENTAL_PMR
- #define PMR_DIAGNOSTIC_PUSH \
-  _Pragma("clang diagnostic push") \
-  _Pragma("clang diagnostic ignored \"-Wdeprecated-declarations\"")
- #define PMR_DIAGNOSTIC_POP \
-  _Pragma("clang diagnostic pop")
-#else
- #define PMR_DIAGNOSTIC_PUSH
- #define PMR_DIAGNOSTIC_POP
-#endif
diff --git a/include/realtime_memory/pmr_shim.h b/include/realtime_memory/pmr_shim.h
new file mode 100644
index 0000000..6b243f6
--- /dev/null
+++ b/include/realtime_memory/pmr_shim.h
@@ -0,0 +1,266 @@
+//==============================================================================
+// Copyright (c) 2019-2026 CradleApps, LLC - All Rights Reserved
+//==============================================================================
+#pragma once
+#include <cstddef>
+#include <limits>
+#include <memory>
+#include <new>
+#include <stdexcept>
+#include <tuple>
+#include <type_traits>
+#include <utility>
+
+/** On macOS std::pmr is available but requires the libc++ from macOS 14.
+ *
+ *  This implementation ensures that memory_resource & polymorphic_allocator
+ *  are available on macOS 10.14 - 13 as well.
+ *
+ *  Care is taken to ensure that everything is header-only to ensure all
+ *  symbols including the vtables are present in consuming object
+ *  files rather than linking on load.
+ */
+namespace rtm_pmr
+{
+class memory_resource;
+}
+
+namespace cradle::pmr
+{
+/** Defined in memory_resources.h. Declared here so that a default-constructed
+ *  polymorphic_allocator picks up the same default resource as the rest of the
+ *  library, rather than keeping a second, independent one.
+ */
+rtm_pmr::memory_resource* get_default_resource() noexcept;
+} // namespace cradle::pmr
+
+namespace rtm_pmr
+{
+//==============================================================================
+/** An abstract interface for classes that encapsulate memory resources. */
+class memory_resource
+{
+public:
+    memory_resource() = default;
+    memory_resource (const memory_resource&) = default;
+    memory_resource& operator= (const memory_resource&) = default;
+
+    /** Defined inline, so this class has no Itanium ABI "key function".
+     *  The vtable is then created in any consuming object file and deduplicated
+     *  at link time.
+     */
+    virtual ~memory_resource() = default;
+
+    void* allocate (std::size_t bytes, std::size_t alignment = alignof (std::max_align_t))
+    {
+        return do_allocate (bytes, alignment);
+    }
+
+    void deallocate (void* p, std::size_t bytes, std::size_t alignment = alignof (std::max_align_t))
+    {
+        do_deallocate (p, bytes, alignment);
+    }
+
+    bool is_equal (const memory_resource& other) const noexcept
+    {
+        return do_is_equal (other);
+    }
+
+private:
+    virtual void* do_allocate (std::size_t bytes, std::size_t alignment) = 0;
+    virtual void do_deallocate (void* p, std::size_t bytes, std::size_t alignment) = 0;
+    virtual bool do_is_equal (const memory_resource& other) const noexcept = 0;
+};
+
+inline bool operator== (const memory_resource& a, const memory_resource& b) noexcept
+{
+    return &a == &b || a.is_equal (b);
+}
+
+inline bool operator!= (const memory_resource& a, const memory_resource& b) noexcept
+{
+    return ! (a == b);
+}
+
+//==============================================================================
+/** An allocator that routes its allocations through a memory_resource, and
+ *  that performs uses-allocator construction so that allocator-aware elements
+ *  inherit the resource.
+ */
+template <class T>
+class polymorphic_allocator
+{
+public:
+    using value_type = T;
+
+    polymorphic_allocator() noexcept
+        : m_resource (cradle::pmr::get_default_resource())
+    {
+    }
+
+    /** Intentionally implicit, matching std::pmr::polymorphic_allocator.
+     */
+    polymorphic_allocator (memory_resource* r) noexcept
+        : m_resource (r)
+    {
+    }
+
+    polymorphic_allocator (const polymorphic_allocator&) = default;
+
+    template <class U>
+    polymorphic_allocator (const polymorphic_allocator<U>& other) noexcept
+        : m_resource (other.resource())
+    {
+    }
+
+    /** Deleted, as in the standard so an allocator's resource is fixed for its lifetime.
+     */
+    polymorphic_allocator& operator= (const polymorphic_allocator&) = delete;
+
+    T* allocate (std::size_t n)
+    {
+        if (n > max_size())
+            throw std::length_error ("polymorphic_allocator<T>::allocate(n) exceeds max_size()");
+
+        return static_cast<T*> (m_resource->allocate (n * sizeof (T), alignof (T)));
+    }
+
+    void deallocate (T* p, std::size_t n)
+    {
+        m_resource->deallocate (p, n * sizeof (T), alignof (T));
+    }
+
+    //==============================================================================
+    template <class U, class... Args>
+    void construct (U* p, Args&&... args)
+    {
+        construct_using_allocator (p, std::forward<Args> (args)...);
+    }
+
+    template <class T1, class T2, class... Args1, class... Args2>
+    void construct (std::pair<T1, T2>* p,
+                    std::piecewise_construct_t,
+                    std::tuple<Args1...> x,
+                    std::tuple<Args2...> y)
+    {
+        ::new (static_cast<void*> (p))
+            std::pair<T1, T2> (std::piecewise_construct,
+                               allocator_args<T1> (std::move (x)),
+                               allocator_args<T2> (std::move (y)));
+    }
+
+    template <class T1, class T2>
+    void construct (std::pair<T1, T2>* p)
+    {
+        construct (p, std::piecewise_construct, std::tuple<>(), std::tuple<>());
+    }
+
+    template <class T1, class T2, class U, class V>
+    void construct (std::pair<T1, T2>* p, U&& x, V&& y)
+    {
+        construct (p,
+                   std::piecewise_construct,
+                   std::forward_as_tuple (std::forward<U> (x)),
+                   std::forward_as_tuple (std::forward<V> (y)));
+    }
+
+    template <class T1, class T2, class U, class V>
+    void construct (std::pair<T1, T2>* p, const std::pair<U, V>& pr)
+    {
+        construct (p,
+                   std::piecewise_construct,
+                   std::forward_as_tuple (pr.first),
+                   std::forward_as_tuple (pr.second));
+    }
+
+    template <class T1, class T2, class U, class V>
+    void construct (std::pair<T1, T2>* p, std::pair<U, V>&& pr)
+    {
+        construct (p,
+                   std::piecewise_construct,
+                   std::forward_as_tuple (std::forward<U> (pr.first)),
+                   std::forward_as_tuple (std::forward<V> (pr.second)));
+    }
+
+    template <class U>
+    void destroy (U* p)
+    {
+        p->~U();
+    }
+
+    polymorphic_allocator select_on_container_copy_construction() const
+    {
+        return polymorphic_allocator();
+    }
+
+    memory_resource* resource() const noexcept { return m_resource; }
+
+private:
+    static constexpr std::size_t max_size() noexcept
+    {
+        return std::numeric_limits<std::size_t>::max() / sizeof (T);
+    }
+
+    template <class U, class... Args>
+    void construct_using_allocator (U* p, Args&&... args)
+    {
+        if constexpr (! std::uses_allocator<U, polymorphic_allocator>::value)
+        {
+            static_assert (std::is_constructible<U, Args...>::value,
+                           "U must be constructible from Args");
+
+            ::new (static_cast<void*> (p)) U (std::forward<Args> (args)...);
+        }
+        else if constexpr (std::is_constructible<U, std::allocator_arg_t, polymorphic_allocator&, Args...>::value)
+        {
+            ::new (static_cast<void*> (p)) U (std::allocator_arg, *this, std::forward<Args> (args)...);
+        }
+        else
+        {
+            static_assert (std::is_constructible<U, Args..., polymorphic_allocator&>::value,
+                           "U uses an allocator but is not constructible from Args plus this allocator");
+
+            ::new (static_cast<void*> (p)) U (std::forward<Args> (args)..., *this);
+        }
+    }
+
+    /** Returns the tuple of arguments to build a U with, with this allocator
+     *  spliced in wherever U expects it (leading, trailing, or not at all).
+     */
+    template <class U, class... Args>
+    auto allocator_args (std::tuple<Args...>&& t)
+    {
+        if constexpr (! std::uses_allocator<U, polymorphic_allocator>::value)
+        {
+            return std::move (t);
+        }
+        else if constexpr (std::is_constructible<U, std::allocator_arg_t, polymorphic_allocator&, Args...>::value)
+        {
+            return std::tuple_cat (std::tuple<std::allocator_arg_t, polymorphic_allocator&> (std::allocator_arg, *this),
+                                   std::move (t));
+        }
+        else
+        {
+            static_assert (std::is_constructible<U, Args..., polymorphic_allocator&>::value,
+                           "U uses an allocator but is not constructible from Args plus this allocator");
+
+            return std::tuple_cat (std::move (t), std::tuple<polymorphic_allocator&> (*this));
+        }
+    }
+
+    memory_resource* m_resource;
+};
+
+template <class T1, class T2>
+bool operator== (const polymorphic_allocator<T1>& a, const polymorphic_allocator<T2>& b) noexcept
+{
+    return *a.resource() == *b.resource();
+}
+
+template <class T1, class T2>
+bool operator!= (const polymorphic_allocator<T1>& a, const polymorphic_allocator<T2>& b) noexcept
+{
+    return ! (a == b);
+}
+
+} // namespace rtm_pmr
diff --git a/include/realtime_memory/polymorphic_allocators.h b/include/realtime_memory/polymorphic_allocators.h
index d5250dc..3e239e1 100644
--- a/include/realtime_memory/polymorphic_allocators.h
+++ b/include/realtime_memory/polymorphic_allocators.h
@@ -6,8 +6,6 @@
 #include "pmr_includes.h"
 #include "memory_resources.h"
 
-PMR_DIAGNOSTIC_PUSH
-
 namespace cradle::pmr
 {
 /** A simple alias would trigger 'undefined symbols for get_default_resource()' on ARM. */
@@ -117,5 +115,3 @@ bool operator!= (const propagating_allocator<ValueType1>& alloc1,
 }
 
 } // cradle::pmr
-
-PMR_DIAGNOSTIC_POP
diff --git a/include/realtime_memory/realtime_memory.h b/include/realtime_memory/realtime_memory.h
index fafd670..7791135 100644
--- a/include/realtime_memory/realtime_memory.h
+++ b/include/realtime_memory/realtime_memory.h
@@ -4,7 +4,7 @@
 /** A fill-in implementation of C++17 <memory_resource>, to get
  *  monotonic_buffer_resource and unsynchronized_pool_resource.
  *
- *  Sadly these haven't made it to libc++ (clang) yet, though MSVC
+ *  These are not available in macOS libc++ pre macOS 14, though MSVC
  *  and newer GCCs have got implementations. This file is intended
  *  to be a drop-in replacement, and it is inspired by the MSVC
  *  and Bloomberg implementations (permissive licenses).
diff --git a/tests/resource_tests.cpp b/tests/resource_tests.cpp
index a223ce0..eb46e4d 100644
--- a/tests/resource_tests.cpp
+++ b/tests/resource_tests.cpp
@@ -11,8 +11,6 @@
 #include "realtime_memory/free_list_resource.h"
 #include "realtime_memory/containers.h"
 
-PMR_DIAGNOSTIC_PUSH
-
 #include <catch2/catch_test_macros.hpp>
 #include <catch2/catch_template_test_macros.hpp>
 #include <catch2/generators/catch_generators.hpp>
@@ -259,8 +257,8 @@ TEST_CASE ("unsynchronized_pool_resource", "[memory_resource]")
     {
         constexpr auto max_u64 = std::numeric_limits<std::size_t>::max();
         constexpr auto max_u32 = (std::size_t) std::numeric_limits<std::uint32_t>::max();
-        const auto maxBlocks = GENERATE (as<size_t>(), 32ul, 1 << 15, max_u64 - 1);
-        const auto largestBlock = GENERATE (as<size_t>(), 32ul, 1 << 15, max_u64 - 1);
+        const auto maxBlocks = GENERATE_COPY (as<size_t>(), 32ul, 1 << 15, max_u64 - 1);
+        const auto largestBlock = GENERATE_COPY (as<size_t>(), 32ul, 1 << 15, max_u64 - 1);
         CAPTURE (maxBlocks, largestBlock);
 
         pmr::pool_options options {maxBlocks, largestBlock};
@@ -908,5 +906,3 @@ TEST_CASE ("unsynchronized_pool_resource overhead limits", "[memory_resource]")
             resource.deallocate (ptr, numBytes, alignment);
     }
 }
-
-PMR_DIAGNOSTIC_POP