diff --git a/devel/build2/files/patch-build2_libbuild2_script_regex.hxx b/devel/build2/files/patch-build2_libbuild2_script_regex.hxx
new file mode 100644
index 000000000000..11abe3d274c0
--- /dev/null
+++ b/devel/build2/files/patch-build2_libbuild2_script_regex.hxx
@@ -0,0 +1,19 @@
+--- build2/libbuild2/script/regex.hxx.orig	2022-12-16 05:41:50 UTC
++++ build2/libbuild2/script/regex.hxx
+@@ -616,11 +616,16 @@ namespace std
+   // to use as an index in some internal cache regardless if the cache is used
+   // for this specialization (and the cache is used only if CharT is char).
+   //
++  // Note that starting with libc++ 20 we get -Winvalid-specialization for
++  // this specialization. But luckily it doesn't seem to be necessary.
++  //
++#if !defined(_LIBCPP_VERSION) || _LIBCPP_VERSION < 20000
+   template <>
+   struct make_unsigned<build2::script::regex::line_char>
+   {
+     using type = build2::script::regex::line_char;
+   };
++#endif
+ 
+   // When used with libc++ the linker complains that it can't find
+   // __match_any_but_newline<line_char>::__exec() function. The problem is