diff --git a/include/qpdf/Buffer.hh b/include/qpdf/Buffer.hh
index 8e2fc8d..928821e 100644
--- a/include/qpdf/Buffer.hh
+++ b/include/qpdf/Buffer.hh
@@ -46,15 +46,13 @@ class Buffer
     QPDF_DLL
     Buffer(std::string& content);
 
-    [[deprecated("Move Buffer or use Buffer::copy instead")]] QPDF_DLL Buffer(Buffer const&);
-    [[deprecated("Move Buffer or use Buffer::copy instead")]] QPDF_DLL Buffer&
-    operator=(Buffer const&);
-
     QPDF_DLL
     Buffer(Buffer&&) noexcept;
     QPDF_DLL
     Buffer& operator=(Buffer&&) noexcept;
     QPDF_DLL
+    ~Buffer();
+    QPDF_DLL
     size_t getSize() const;
     QPDF_DLL
     unsigned char const* getBuffer() const;
@@ -65,29 +63,8 @@ class Buffer
     QPDF_DLL
     Buffer copy() const;
 
-    // Only used during CI testing.
-    // ABI: remove when removing copy constructor / assignment operator
-    static void setTestMode() noexcept;
-
   private:
-    class Members
-    {
-        friend class Buffer;
-
-      public:
-        QPDF_DLL
-        ~Members();
-
-      private:
-        Members(size_t size, unsigned char* buf, bool own_memory);
-        Members(std::string&& content);
-        Members(Members const&) = delete;
-
-        std::string str;
-        bool own_memory;
-        size_t size;
-        unsigned char* buf;
-    };
+    class Members;
 
     void copy(Buffer const&);
 
diff --git a/libqpdf/Buffer.cc b/libqpdf/Buffer.cc
index 20453a4..26041af 100644
--- a/libqpdf/Buffer.cc
+++ b/libqpdf/Buffer.cc
@@ -4,16 +4,23 @@
 
 #include <cstring>
 
-bool test_mode = false;
-
-// During CI the Buffer copy constructor and copy assignment operator throw an assertion error to
-// detect their accidental use. Call setTestMode to surpress the assertion errors for testing of
-// copy construction and assignment.
-void
-Buffer::setTestMode() noexcept
+class Buffer::Members
 {
-    test_mode = true;
-}
+    friend class Buffer;
+
+  public:
+    ~Members();
+
+  private:
+    Members(size_t size, unsigned char* buf, bool own_memory);
+    Members(std::string&& content);
+    Members(Members const&) = delete;
+
+    std::string str;
+    bool own_memory;
+    size_t size;
+    unsigned char* buf;
+};
 
 Buffer::Members::Members(size_t size, unsigned char* buf, bool own_memory) :
     own_memory(own_memory),
@@ -67,20 +74,6 @@ Buffer::Buffer(std::string& content) :
 {
 }
 
-Buffer::Buffer(Buffer const& rhs)
-{
-    assert(test_mode);
-    copy(rhs);
-}
-
-Buffer&
-Buffer::operator=(Buffer const& rhs)
-{
-    assert(test_mode);
-    copy(rhs);
-    return *this;
-}
-
 Buffer::Buffer(Buffer&& rhs) noexcept :
     m(std::move(rhs.m))
 {
@@ -93,6 +86,8 @@ Buffer::operator=(Buffer&& rhs) noexcept
     return *this;
 }
 
+Buffer::~Buffer() = default;
+
 void
 Buffer::copy(Buffer const& rhs)
 {
diff --git a/libtests/buffer.cc b/libtests/buffer.cc
index 1b87bb7..4326901 100644
--- a/libtests/buffer.cc
+++ b/libtests/buffer.cc
@@ -18,130 +18,65 @@ uc(char const* s)
 int
 main()
 {
-    {
-        // Test that buffers can be copied by value using Buffer::copy.
-        Buffer bc1(2);
-        unsigned char* bc1p = bc1.getBuffer();
-        bc1p[0] = 'Q';
-        bc1p[1] = 'W';
-        Buffer bc2(bc1.copy());
-        bc1p[0] = 'R';
-        unsigned char* bc2p = bc2.getBuffer();
-        assert(bc2p != bc1p);
-        assert(bc2p[0] == 'Q');
-        assert(bc2p[1] == 'W');
-        bc2 = bc1.copy();
-        bc2p = bc2.getBuffer();
-        assert(bc2p != bc1p);
-        assert(bc2p[0] == 'R');
-        assert(bc2p[1] == 'W');
-
-        // Test Buffer(std:string&&)
-        Buffer bc3("QW");
-        unsigned char* bc3p = bc3.getBuffer();
-        Buffer bc4(bc3.copy());
-        bc3p[0] = 'R';
-        unsigned char* bc4p = bc4.getBuffer();
-        assert(bc4p != bc3p);
-        assert(bc4p[0] == 'Q');
-        assert(bc4p[1] == 'W');
-        bc4 = bc3.copy();
-        bc4p = bc4.getBuffer();
-        assert(bc4p != bc3p);
-        assert(bc4p[0] == 'R');
-        assert(bc4p[1] == 'W');
-    }
-
-#ifdef _MSC_VER
-# pragma warning(disable : 4996)
-#endif
-#if (defined(__GNUC__) || defined(__clang__))
-# pragma GCC diagnostic push
-# pragma GCC diagnostic ignored "-Wdeprecated-declarations"
-#endif
-    {
-        // Test that buffers can be copied by value using copy construction / assignment.
-        Buffer::setTestMode();
-        Buffer bc1(2);
-        unsigned char* bc1p = bc1.getBuffer();
-        bc1p[0] = 'Q';
-        bc1p[1] = 'W';
-        Buffer bc2(bc1);
-        bc1p[0] = 'R';
-        unsigned char* bc2p = bc2.getBuffer();
-        assert(bc2p != bc1p);
-        assert(bc2p[0] == 'Q');
-        assert(bc2p[1] == 'W');
-        bc2 = bc1;
-        bc2p = bc2.getBuffer();
-        assert(bc2p != bc1p);
-        assert(bc2p[0] == 'R');
-        assert(bc2p[1] == 'W');
-
-        // Test Buffer(std:string&&)
-        Buffer bc3("QW");
-        unsigned char* bc3p = bc3.getBuffer();
-        Buffer bc4(bc3);
-        bc3p[0] = 'R';
-        unsigned char* bc4p = bc4.getBuffer();
-        assert(bc4p != bc3p);
-        assert(bc4p[0] == 'Q');
-        assert(bc4p[1] == 'W');
-        bc4 = bc3;
-        bc4p = bc4.getBuffer();
-        assert(bc4p != bc3p);
-        assert(bc2p[0] == 'R');
-        assert(bc2p[1] == 'W');
-
-        // Test Buffer(std:string&)
-        std::string s{"QW"};
-        Buffer bc5(s);
-        unsigned char* bc5p = bc5.getBuffer();
-        Buffer bc6(bc5);
-        bc5p[0] = 'R';
-        unsigned char* bc6p = bc6.getBuffer();
-        assert(bc6p != bc5p);
-        assert(bc6p[0] == 'Q');
-        assert(bc6p[1] == 'W');
-        bc6 = bc5;
-        bc6p = bc6.getBuffer();
-        assert(bc6p != bc5p);
-        assert(bc2p[0] == 'R');
-        assert(bc2p[1] == 'W');
-    }
-#if (defined(__GNUC__) || defined(__clang__))
-# pragma GCC diagnostic pop
-#endif
-
-    {
-        // Test that buffers can be moved.
-        Buffer bm1(2);
-        unsigned char* bm1p = bm1.getBuffer();
-        bm1p[0] = 'Q';
-        bm1p[1] = 'W';
-        Buffer bm2(std::move(bm1));
-        bm1p[0] = 'R';
-        unsigned char* bm2p = bm2.getBuffer();
-        assert(bm2p == bm1p);
-        assert(bm2p[0] == 'R');
-
-        Buffer bm3 = std::move(bm2);
-        unsigned char* bm3p = bm3.getBuffer();
-        assert(bm3p == bm2p);
-
-        // Test Buffer(dtd::string&&)
-        Buffer bm4("QW");
-        unsigned char* bm4p = bm4.getBuffer();
-        Buffer bm5(std::move(bm4));
-        bm4p[0] = 'R';
-        unsigned char* bm5p = bm5.getBuffer();
-        assert(bm5p == bm4p);
-        assert(bm5p[0] == 'R');
-
-        Buffer bm6 = std::move(bm5);
-        unsigned char* bm6p = bm6.getBuffer();
-        assert(bm6p == bm5p);
-    }
+    // Test that buffers can be copied by value using Buffer::copy.
+    Buffer bc1(2);
+    unsigned char* bc1p = bc1.getBuffer();
+    bc1p[0] = 'Q';
+    bc1p[1] = 'W';
+    Buffer bc2(bc1.copy());
+    bc1p[0] = 'R';
+    unsigned char* bc2p = bc2.getBuffer();
+    assert(bc2p != bc1p);
+    assert(bc2p[0] == 'Q');
+    assert(bc2p[1] == 'W');
+    bc2 = bc1.copy();
+    bc2p = bc2.getBuffer();
+    assert(bc2p != bc1p);
+    assert(bc2p[0] == 'R');
+    assert(bc2p[1] == 'W');
+
+    // Test Buffer(std:string&&)
+    Buffer bc3("QW");
+    unsigned char* bc3p = bc3.getBuffer();
+    Buffer bc4(bc3.copy());
+    bc3p[0] = 'R';
+    unsigned char* bc4p = bc4.getBuffer();
+    assert(bc4p != bc3p);
+    assert(bc4p[0] == 'Q');
+    assert(bc4p[1] == 'W');
+    bc4 = bc3.copy();
+    bc4p = bc4.getBuffer();
+    assert(bc4p != bc3p);
+    assert(bc4p[0] == 'R');
+    assert(bc4p[1] == 'W');
+
+    // Test that buffers can be moved.
+    Buffer bm1(2);
+    unsigned char* bm1p = bm1.getBuffer();
+    bm1p[0] = 'Q';
+    bm1p[1] = 'W';
+    Buffer bm2(std::move(bm1));
+    bm1p[0] = 'R';
+    unsigned char* bm2p = bm2.getBuffer();
+    assert(bm2p == bm1p);
+    assert(bm2p[0] == 'R');
+
+    Buffer bm3 = std::move(bm2);
+    unsigned char* bm3p = bm3.getBuffer();
+    assert(bm3p == bm2p);
+
+    // Test Buffer(dtd::string&&)
+    Buffer bm4("QW");
+    unsigned char* bm4p = bm4.getBuffer();
+    Buffer bm5(std::move(bm4));
+    bm4p[0] = 'R';
+    unsigned char* bm5p = bm5.getBuffer();
+    assert(bm5p == bm4p);
+    assert(bm5p[0] == 'R');
+
+    Buffer bm6 = std::move(bm5);
+    unsigned char* bm6p = bm6.getBuffer();
+    assert(bm6p == bm5p);
 
     try {
         Pl_Discard discard;
diff --git a/manual/release-notes.rst b/manual/release-notes.rst
index b60ed19..c5522ba 100644
--- a/manual/release-notes.rst
+++ b/manual/release-notes.rst
@@ -9,18 +9,20 @@ For a detailed list of changes, please see the file
 
 Planned changes for future 12.x (subject to change):
 
-  - ``Buffer`` copy constructor and assignment operator will be
-    removed. ``Buffer`` copy operations are expensive as they always
-    involve copying the buffer content. Use ``buffer2 =
-    buffer1.copy();`` or ``Buffer buffer2{buffer1.copy()};`` to make
-    it explicit that copying is intended.
-
   - ``QIntC.hh`` contains the type ``substract``, which will be fixed
     to ``subtract``. (Not enabled with ``FUTURE`` option.)
 
 .. x.y.z: not yet released
 
 12.0.0: not yet released
+  - API: breaking changes
+
+    - ``Buffer`` copy constructor and assignment operator have been
+      removed. ``Buffer`` copy operations are expensive as they always
+      involve copying the buffer content. Use ``buffer2 = buffer1.copy();``
+      or ``Buffer buffer2{buffer1.copy()};`` to make it explicit that
+      copying is intended.
+
   - Library Enhancements
 
     - ``QPDFObjectHandle`` supports move construction/assignment.