From e220c66bc70d5641a0bff182b7c570ad01449381 Mon Sep 17 00:00:00 2001
From: David Bold <dave@ipp.mpg.de>
Date: Wed, 11 Mar 2026 12:55:37 +0100
Subject: [PATCH] Prevent accidential overwriting of parallel slices

---
 src/field/field3d.cxx     | 1 +
 src/mesh/parallel/fci.cxx | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/field/field3d.cxx b/src/field/field3d.cxx
index da7bd494c9..2087bca582 100644
--- a/src/field/field3d.cxx
+++ b/src/field/field3d.cxx
@@ -343,6 +343,7 @@ Field3D& Field3D::operator=(const BoutReal val) {
 }
 
 void Field3D::calcParallelSlices() {
+  ASSERT1(areCalcParallelSlicesAllowed());
   getCoordinates()->getParallelTransform().calcParallelSlices(*this);
 }
 
diff --git a/src/mesh/parallel/fci.cxx b/src/mesh/parallel/fci.cxx
index 152ffaed2d..fa965a335a 100644
--- a/src/mesh/parallel/fci.cxx
+++ b/src/mesh/parallel/fci.cxx
@@ -378,7 +378,7 @@ void FCITransform::checkInputGrid() {
 }
 
 void FCITransform::calcParallelSlices(Field3D& f) {
-
+  ASSERT1(f.areCalcParallelSlicesAllowed());
   ASSERT1(f.getDirectionY() == YDirectionType::Standard);
   // Only have forward_map/backward_map for CELL_CENTRE, so can only deal with
   // CELL_CENTRE inputs