diff --git a/math/libmesh/files/patch-src_utils_xdr__cxx.C b/math/libmesh/files/patch-src_utils_xdr__cxx.C
new file mode 100644
index 000000000000..c55903a941cb
--- /dev/null
+++ b/math/libmesh/files/patch-src_utils_xdr__cxx.C
@@ -0,0 +1,28 @@
+-- Fix build on FreeBSD 16 where xdrproc_t changed from a variadic to a
+-- two-argument function pointer type, so calling it with three arguments fails.
+
+--- src/utils/xdr_cxx.C.orig	2026-07-19 04:45:48 UTC
++++ src/utils/xdr_cxx.C
+@@ -28,6 +28,9 @@
+ #include "libmesh/xdr_cxx.h"
+ #include "libmesh/libmesh_logging.h"
+ #ifdef LIBMESH_HAVE_GZSTREAM
++#ifdef __FreeBSD__
++# include <sys/param.h>
++#endif
+ # include "libmesh/ignore_warnings.h" // shadowing in gzstream.h
+ # include "gzstream.h" // For reading/writing compressed streams
+ # include "libmesh/restore_warnings.h"
+@@ -484,7 +487,12 @@ bool xdr_translate(XDR * x, T & a)
+ template <typename T>
+ bool xdr_translate(XDR * x, T & a)
+ {
++#if defined(__FreeBSD__) && __FreeBSD_version >= 1600000
++  // FreeBSD 16 changed xdrproc_t to a two-argument function pointer.
++  return (xdr_translator<T>())(x, &a);
++#else
+   return (xdr_translator<T>())(x, &a, 0);
++#endif
+ }
+
+ template <>