diff --git a/Formula/kssd.rb b/Formula/kssd.rb
index ce23d7616..e288a23c1 100644
--- a/Formula/kssd.rb
+++ b/Formula/kssd.rb
@@ -1,8 +1,8 @@
 class Kssd < Formula
   desc "K-mer substring space sampling/shuffling decomposition"
   homepage "https://github.com/yhg926/public_kssd"
-  url "https://github.com/yhg926/public_kssd/archive/refs/tags/v1.1.tar.gz"
-  sha256 "bdf42a9a280126c41736aa9ee480d2948e32f9027e97607fe18473db59187bf4"
+  url "https://github.com/yhg926/public_kssd/archive/refs/tags/v2.21.tar.gz"
+  sha256 "2f6217b6e685dbe15c9aa4fa9a7eeb225651eb608f34799efea4ce84e2d0fd86"
 
   bottle do
     root_url "https://ghcr.io/v2/brewsci/bio"
@@ -13,6 +13,11 @@ class Kssd < Formula
   depends_on :linux
   depends_on "zlib"
 
+  # Fix a heap off-by-one (long_domain buffer too small by 1) that aborts with
+  # "buffer overflow detected" under glibc _FORTIFY_SOURCE=3, and bump the
+  # internal version banner (upstream left it at 2.2).
+  patch :DATA
+
   def install
     system "make"
     bin.install "kssd"
@@ -23,3 +28,24 @@ def install
     assert_match version.to_s, shell_output("#{bin}/kssd -V 2>&1")
   end
 end
+__END__
+--- a/kssd.c
++++ b/kssd.c
+@@ -17,7 +17,7 @@
+ #include <stdlib.h>
+ #include <string.h>
+ #include "global_basic.h"
+-const char *argp_program_version = "kssd version 2.2";
++const char *argp_program_version = "kssd version 2.21";
+ const char *argp_program_bug_address = "yhg926@gmail.com";
+ int main(int argc, char** argv)
+ {
+@@ -26,7 +26,7 @@
+  const char subcommand_n[] = "<subcommand>";
+   domain = (char*) malloc(strlen(argv[0])+1);
+   strcpy(domain,argv[0]);
+-  long_domain = (char*) malloc( strlen(domain) + strlen(subcommand_n) + 1);
++  long_domain = (char*) malloc( strlen(domain) + strlen(subcommand_n) + 2);
+   snprintf(long_domain,strlen(domain) + strlen(subcommand_n) + 2,"%s %s",domain,subcommand_n);
+   cmd_global(argc, argv);
+   return 0;