From 977edcfc102b861d5a3c8976a94f5fd33aeac53f Mon Sep 17 00:00:00 2001
From: Ardavan Oskooi <ardavan.oskooi@gmail.com>
Date: Sun, 26 Apr 2026 14:55:27 -0700
Subject: [PATCH] fix thread-safety for user-defined epsilon in meepgeom.cpp

---
 src/meepgeom.cpp | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/meepgeom.cpp b/src/meepgeom.cpp
index 5ec74587a..791c2bdc9 100644
--- a/src/meepgeom.cpp
+++ b/src/meepgeom.cpp
@@ -658,7 +658,8 @@ geom_epsilon::geom_epsilon(geometric_object_list g, material_type_list mlist,
   int length = g.num_items;
   geometry.num_items = length;
   geometry.items = new geometric_object[length];
-  has_user_materials = false;
+  has_user_materials = default_material && ((material_type)default_material)->which_subclass ==
+                                               material_data::MATERIAL_USER;
   for (int i = 0; i < length; i++) {
     geometric_object_copy(&g.items[i], &geometry.items[i]);
     geometry.items[i].material = new material_data();