diff --git a/Doc/c-api/unicode.rst b/Doc/c-api/unicode.rst
index ef180464ef1688..45f50ba5f97d26 100644
--- a/Doc/c-api/unicode.rst
+++ b/Doc/c-api/unicode.rst
@@ -1461,10 +1461,6 @@ the user settings on the machine running the codec.
    .. versionadded:: 3.3
 
 
-Methods & Slots
-"""""""""""""""
-
-
 .. _unicodemethodsandslots:
 
 Methods and Slot Functions
diff --git a/Doc/library/ast.rst b/Doc/library/ast.rst
index ca9a6b0712c9a2..cf22250cac6091 100644
--- a/Doc/library/ast.rst
+++ b/Doc/library/ast.rst
@@ -268,9 +268,9 @@ Literals
 .. class:: Constant(value)
 
    A constant value. The ``value`` attribute of the ``Constant`` literal contains the
-   Python object it represents. The values represented can be simple types
-   such as a number, string or ``None``, but also immutable container types
-   (tuples and frozensets) if all of their elements are constant.
+   Python object it represents. The values represented can be instances of :class:`str`,
+   :class:`bytes`, :class:`int`, :class:`float`, :class:`complex`, and :class:`bool`,
+   and the constants :data:`None` and :data:`Ellipsis`.
 
    .. doctest::
 
diff --git a/Doc/library/compression.zstd.rst b/Doc/library/compression.zstd.rst
index 1e1802155a19ec..35bcbc2bfd8eac 100644
--- a/Doc/library/compression.zstd.rst
+++ b/Doc/library/compression.zstd.rst
@@ -615,6 +615,24 @@ Advanced parameter control
 
       A value of zero causes the value to be selected automatically.
 
+   .. attribute:: content_size_flag
+
+      Write the size of the data to be compressed into the Zstandard frame
+      header when known prior to compressing.
+
+      This flag only takes effect under the following two scenarios:
+
+      * Calling :func:`compress` for one-shot compression
+      * Providing all of the data to be compressed in the frame in a single
+        :meth:`ZstdCompressor.compress` call, with the
+        :attr:`ZstdCompressor.FLUSH_FRAME` mode.
+
+      All other compression calls may not write the size information into the
+      frame header.
+
+      ``True`` or ``1`` enable the content size flag while ``False`` or ``0``
+      disable it.
+
    .. attribute:: checksum_flag
 
       A four-byte checksum using XXHash64 of the uncompressed content is
diff --git a/Misc/NEWS.d/next/Library/2025-05-29-06-53-40.gh-issue-134885.-_L22o.rst b/Misc/NEWS.d/next/Library/2025-05-29-06-53-40.gh-issue-134885.-_L22o.rst
new file mode 100644
index 00000000000000..4b05d42c109d06
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2025-05-29-06-53-40.gh-issue-134885.-_L22o.rst
@@ -0,0 +1,2 @@
+Fix possible crash in the :mod:`compression.zstd` module related to setting
+parameter types. Patch by Jelle Zijlstra.
diff --git a/Modules/_zstd/_zstdmodule.c b/Modules/_zstd/_zstdmodule.c
index 5ad697d2b83dd6..986b3579479f0f 100644
--- a/Modules/_zstd/_zstdmodule.c
+++ b/Modules/_zstd/_zstdmodule.c
@@ -514,13 +514,10 @@ _zstd_set_parameter_types_impl(PyObject *module, PyObject *c_parameter_type,
         return NULL;
     }
 
-    Py_XDECREF(mod_state->CParameter_type);
-    Py_INCREF(c_parameter_type);
-    mod_state->CParameter_type = (PyTypeObject*)c_parameter_type;
-
-    Py_XDECREF(mod_state->DParameter_type);
-    Py_INCREF(d_parameter_type);
-    mod_state->DParameter_type = (PyTypeObject*)d_parameter_type;
+    Py_XSETREF(
+        mod_state->CParameter_type, (PyTypeObject*)Py_NewRef(c_parameter_type));
+    Py_XSETREF(
+        mod_state->DParameter_type, (PyTypeObject*)Py_NewRef(d_parameter_type));
 
     Py_RETURN_NONE;
 }
diff --git a/Modules/_zstd/compressor.c b/Modules/_zstd/compressor.c
index 0fc3d7d36c68fe..8ff2a3aadc1cd6 100644
--- a/Modules/_zstd/compressor.c
+++ b/Modules/_zstd/compressor.c
@@ -512,7 +512,7 @@ compress_lock_held(ZstdCompressor *self, Py_buffer *data,
     return NULL;
 }
 
-#ifdef Py_DEBUG
+#ifndef NDEBUG
 static inline int
 mt_continue_should_break(ZSTD_inBuffer *in, ZSTD_outBuffer *out)
 {