From c6ef84d1d5ad47cc528573332a539ea1f25a8e44 Mon Sep 17 00:00:00 2001
From: Kevin Sawatzky <66632997+nuclearkevin@users.noreply.github.com>
Date: Sun, 15 Feb 2026 15:59:08 -0600
Subject: [PATCH] Set upper and lower interpolation bounds for MGXS data.
 (#3803)

---
 src/mgxs.cpp | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/mgxs.cpp b/src/mgxs.cpp
index a2c479f21..ea78238b8 100644
--- a/src/mgxs.cpp
+++ b/src/mgxs.cpp
@@ -14,6 +14,7 @@
 #include "openmc/error.h"
 #include "openmc/math_functions.h"
 #include "openmc/mgxs_interface.h"
+#include "openmc/nuclide.h"
 #include "openmc/random_lcg.h"
 #include "openmc/settings.h"
 #include "openmc/string_utils.h"
@@ -85,6 +86,13 @@ void Mgxs::metadata_from_hdf5(hid_t xs_id, const vector<double>& temperature,
   delete[] dset_names;
   std::sort(temps_available.begin(), temps_available.end());
 
+  // Set the global upper and lower interpolation bounds to avoid errors
+  // involving C-API functions.
+  data::temperature_min =
+    std::min(data::temperature_min, temps_available.front());
+  data::temperature_max =
+    std::max(data::temperature_max, temps_available.back());
+
   // If only one temperature is available, lets just use nearest temperature
   // interpolation
   if ((num_temps == 1) &&