1 files changed, 21 insertions, 4 deletions
diff --git a/macros/latex/contrib/l3packages/xparse.dtx b/macros/latex/contrib/l3packages/xparse.dtx
index 62ac19ff25..ac0ee03d3f 100644
--- a/macros/latex/contrib/l3packages/xparse.dtx
+++ b/macros/latex/contrib/l3packages/xparse.dtx
@@ -67,7 +67,7 @@
 %    }^^A
 % }
 %
-% \date{Released 2024-05-08}
+% \date{Released 2024-08-16}
 %
 % \maketitle
 %
@@ -1079,7 +1079,7 @@
 %    \end{macrocode}
 %
 %    \begin{macrocode}
-\ProvidesExplPackage{xparse}{2024-05-08}{}
+\ProvidesExplPackage{xparse}{2024-08-16}{}
   {L3 Experimental document command parser}
 %    \end{macrocode}
 %
@@ -1436,13 +1436,30 @@
 %
 % \begin{macro}{\@@_get_arg_spec:NTF}
 %   If the command is not an \pkg{xparse} command, complain.  If it is,
-%   its second \enquote{item} is the argument specification.
+%   its second \enquote{item} is the argument specification unless the
+%   command is optimised: in the latter case, we can reconstruct the
+%   spec.
 %    \begin{macrocode}
 \cs_gset_protected:Npn \@@_get_arg_spec:NTF #1#2#3
   {
     \__kernel_cmd_if_xparse:NTF #1
       {
-        \tl_set:Ne \ArgumentSpecification { \tl_item:Nn #1 { 2 } }
+        \tl_set:Ne \ArgumentSpecification
+          {
+            \exp_args:No \tl_if_head_eq_meaning:nNTF {#1} \@@_start_optimized:
+              {
+                \prg_replicate:nn
+                  {
+                    \str_count:e
+                      {
+                        \exp_args:Nc \cs_parameter_spec:N
+                          { \cs_to_str:N #1 \c_space_tl code }
+                      } / 2
+                  }
+                  { m }
+              }
+              { \tl_item:Nn #1 { 2 } }
+          }
         #2
       }
       {#3}