diff --git a/devel/build2/files/patch-build2_libbuild2_cc_guess.cxx b/devel/build2/files/patch-build2_libbuild2_cc_guess.cxx
new file mode 100644
index 000000000000..6721fdcbc86d
--- /dev/null
+++ b/devel/build2/files/patch-build2_libbuild2_cc_guess.cxx
@@ -0,0 +1,79 @@
+commit 0e1b73e3b43bca7c1d77ed669b364819ad211da9
+Author: Boris Kolpackov <boris@codesynthesis.com>
+Date:   2024-02-02T11:41:33+02:00
+
+    Handle unseparated `rc` and `git` suffixes in Clang version (GH issue #360)
+
+--- build2/libbuild2/cc/guess.cxx.orig	2023-06-19 05:26:33 UTC
++++ build2/libbuild2/cc/guess.cxx
+@@ -2421,6 +2421,12 @@ namespace build2
+       //
+       // emcc (...) 2.0.8
+       //
++      // Pre-releases of the vanilla Clang append `rc` or `git` to the
++      // version, unfortunately without a separator. So we will handle these
++      // ad hoc. For example:
++      //
++      // FreeBSD clang version 18.1.0rc (https://github.com/llvm/llvm-project.git llvmorg-18-init-18361-g22683463740e)
++      //
+       auto extract_version = [] (const string& s, bool patch, const char* what)
+         -> compiler_version
+       {
+@@ -2435,8 +2441,28 @@ namespace build2
+           // end of the word position (first space). In fact, we can just
+           // check if it is >= e.
+           //
+-          if (s.find_first_not_of ("1234567890.", b, 11) >= e)
++          size_t p (s.find_first_not_of ("1234567890.", b, 11));
++          if (p >= e)
+             break;
++
++          // Handle the unseparated `rc` and `git` suffixes.
++          //
++          if (p != string::npos)
++          {
++            if (p + 2 == e && (e - b) > 2 &&
++                s[p] == 'r' && s[p + 1] == 'c')
++            {
++              e -= 2;
++              break;
++            }
++
++            if (p + 3 == e && (e - b) > 3 &&
++                s[p] == 'g' && s[p + 1] == 'i' && s[p + 2] == 't')
++            {
++              e -= 3;
++              break;
++            }
++          }
+         }
+ 
+         if (b == e)
+@@ -2472,8 +2498,15 @@ namespace build2
+         ver.patch = next ("patch", patch);
+ 
+         if (e != s.size ())
+-          ver.build.assign (s, e + 1, string::npos);
++        {
++          // Skip the separator (it could also be unseparated `rc` or `git`).
++          //
++          if (s[e] == ' ' || s[e] == '-')
++            e++;
+ 
++          ver.build.assign (s, e, string::npos);
++        }
++
+         return ver;
+       };
+ 
+@@ -2496,7 +2529,10 @@ namespace build2
+ 
+         // Some overrides for testing.
+         //
++        //string s (xv != nullptr ? *xv : "");
++        //
+         //s = "clang version 3.7.0 (tags/RELEASE_370/final)";
++        //s = "FreeBSD clang version 18.1.0rc (https://github.com/llvm/llvm-project.git llvmorg-18-init-18361-g22683463740e)";
+         //
+         //gr.id.variant = "apple";
+         //s = "Apple LLVM version 7.3.0 (clang-703.0.16.1)";