diff --git a/libstdc++-v3/doc/html/manual/api.html b/libstdc++-v3/doc/html/manual/api.html
index 7d5f754fb38..27c0d090e5d 100644
--- a/libstdc++-v3/doc/html/manual/api.html
+++ b/libstdc++-v3/doc/html/manual/api.html
@@ -370,6 +370,11 @@ Calling a <code class="code">std::bind</code> result as volatile was deprecated
   For the non-default <code class="option">--enable-symvers=gnu-versioned-namespace</code>
   configuration, the shared library SONAME has been changed to
   <code class="filename">libstdc++.so.8</code>.
+</p><p>
+  The extension allowing containers to be instantiated with an allocator
+  that doesn't match the container's value type is no longer allowed in
+  strict (<code class="option">-std=c++NN</code>) modes, only in
+  <code class="option">-std=gnu++NN</code> modes.
 </p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="api.rel_91"></a><code class="constant">9</code></h3></div></div></div><p>
   C++17 header
   <code class="filename">&lt;memory_resource&gt;</code>
@@ -425,6 +430,10 @@ Calling a <code class="code">std::bind</code> result as volatile was deprecated
   and
   <code class="filename">&lt;stop_token&gt;</code>
   added.
+</p><p>
+  The extension allowing containers to be instantiated with an allocator
+  that doesn't match the container's value type is no longer allowed in
+  C++20 mode, even in non-strict <code class="option">-std=gnu++20</code> mode.
 </p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="api.rel_111"></a><code class="constant">11</code></h3></div></div></div><p>
   The <code class="option">--enable-cheaders=c_std</code> configuration
   was deprecated.
@@ -479,4 +488,8 @@ Tunables <span style="color: red">&lt;variable&gt;glibcxx.eh_pool.obj_count&lt;/
 </p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="api.rel_141"></a><code class="constant">14</code></h3></div></div></div><p>
 Deprecate the non-standard overload that allows <code class="code">std::setfill</code>
 to be used with <code class="code">std::basic_istream</code>.
+</p><p>
+  The extension allowing <code class="code">std::basic_string</code> to be instantiated
+  with an allocator that doesn't match the string's character type is no
+  longer allowed in C++20 mode.
 </p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="abi.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="appendix_porting.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="backwards.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">ABI Policy and Guidelines </td><td width="20%" align="center"><a accesskey="h" href="../index.html">Home</a></td><td width="40%" align="right" valign="top"> Backwards Compatibility</td></tr></table></div></body></html>
\ No newline at end of file
diff --git a/libstdc++-v3/doc/xml/manual/evolution.xml b/libstdc++-v3/doc/xml/manual/evolution.xml
index 4037a18d2df..db70f24f2f9 100644
--- a/libstdc++-v3/doc/xml/manual/evolution.xml
+++ b/libstdc++-v3/doc/xml/manual/evolution.xml
@@ -915,6 +915,13 @@ Calling a <code>std::bind</code> result as volatile was deprecated for C++17.
   <filename>libstdc++.so.8</filename>.
 </para>
 
+<para>
+  The extension allowing containers to be instantiated with an allocator
+  that doesn't match the container's value type is no longer allowed in
+  strict (<option>-std=c++NN</option>) modes, only in
+  <option>-std=gnu++NN</option> modes.
+</para>
+
 </section>
 
 <section xml:id="api.rel_91"><info><title><constant>9</constant></title></info>
@@ -998,6 +1005,12 @@ Calling a <code>std::bind</code> result as volatile was deprecated for C++17.
   added.
 </para>
 
+<para>
+  The extension allowing containers to be instantiated with an allocator
+  that doesn't match the container's value type is no longer allowed in
+  C++20 mode, even in non-strict <option>-std=gnu++20</option> mode.
+</para>
+
 </section>
 
 <section xml:id="api.rel_111"><info><title><constant>11</constant></title></info>
@@ -1096,6 +1109,12 @@ Deprecate the non-standard overload that allows <code>std::setfill</code>
 to be used with <code>std::basic_istream</code>.
 </para>
 
+<para>
+  The extension allowing <code>std::basic_string</code> to be instantiated
+  with an allocator that doesn't match the string's character type is no
+  longer allowed in C++20 mode.
+</para>
+
 </section>
 
 </section>