From e26c1707eef3b23eaf4a44b911b00e53a93785ca Mon Sep 17 00:00:00 2001
From: "Steven G. Johnson" <stevenj@alum.mit.edu>
Date: Thu, 11 Aug 2022 09:25:51 -0400
Subject: [PATCH] fix NanoComp/meep#2189

---
 src/maxwell/maxwell_eps.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/maxwell/maxwell_eps.c b/src/maxwell/maxwell_eps.c
index 145e240..e7ff93f 100644
--- a/src/maxwell/maxwell_eps.c
+++ b/src/maxwell/maxwell_eps.c
@@ -585,7 +585,7 @@ void set_maxwell_dielectric(maxwell_data *md,
 	     r[1] = i2 * s2;
 	     r[2] = i3 * s3;
 
-       if (mesh_prod == 1) {
+       if (epsilon && mesh_prod == 1) {
          epsilon(&eps_mean, &eps_inv_mean, r, epsilon_data);
          md->eps_inv[xyz_index] = eps_inv_mean;
          goto got_eps_inv;