diff --git a/test/emu/common/instr.h b/test/emu/common/instr.h
index 37c05c8..f5c0d52 100644
--- a/test/emu/common/instr.h
+++ b/test/emu/common/instr.h
@@ -1,4 +1,4 @@
-/* Copyright (c) 2021-2023 Barcelona Supercomputing Center (BSC)
+/* Copyright (c) 2021-2024 Barcelona Supercomputing Center (BSC)
  * SPDX-License-Identifier: GPL-3.0-or-later */
 
 #ifndef INSTR_H
@@ -62,6 +62,7 @@ int64_t get_delta(void);
 	}
 
 INSTR_3ARG(instr_thread_execute, "OHx", int32_t, cpu, int32_t, creator_tid, uint64_t, tag)
+INSTR_1ARG(instr_thread_affinity_set, "OAs", int32_t, cpu)
 
 static inline void
 instr_thread_end(void)
diff --git a/test/emu/nanos6/CMakeLists.txt b/test/emu/nanos6/CMakeLists.txt
index d8fec56..11b58f4 100644
--- a/test/emu/nanos6/CMakeLists.txt
+++ b/test/emu/nanos6/CMakeLists.txt
@@ -1,4 +1,4 @@
-# Copyright (c) 2022-2023 Barcelona Supercomputing Center (BSC)
+# Copyright (c) 2022-2024 Barcelona Supercomputing Center (BSC)
 # SPDX-License-Identifier: GPL-3.0-or-later
 
 test_emu(nested-tasks.c)
@@ -14,5 +14,6 @@ test_emu(switch-same-type.c)
 test_emu(sponge.c)
 test_emu(sponge-breakdown.c BREAKDOWN)
 test_emu(breakdown-no-black.c BREAKDOWN)
+test_emu(breakdown-write-zero.c MP BREAKDOWN)
 test_emu(rerun-task-bad.c SHOULD_FAIL
   REGEX "body_execute: body(id=1,taskid=1) is not allowed to run again")
diff --git a/test/emu/nanos6/breakdown-write-zero.c b/test/emu/nanos6/breakdown-write-zero.c
new file mode 100644
index 0000000..c67a552
--- /dev/null
+++ b/test/emu/nanos6/breakdown-write-zero.c
@@ -0,0 +1,35 @@
+/* Copyright (c) 2024 Barcelona Supercomputing Center (BSC)
+ * SPDX-License-Identifier: GPL-3.0-or-later */
+
+#include <stdint.h>
+#include <stdlib.h>
+#include "compat.h"
+#include "instr.h"
+#include "instr_nanos6.h"
+
+/* Cause the sort module to write zeros in some rows when the breakdown model is
+ * enabled, which shouldn't cause a panic. */
+int
+main(void)
+{
+	int rank = atoi(getenv("OVNI_RANK"));
+	int nranks = atoi(getenv("OVNI_NRANKS"));
+
+	if (nranks < 2)
+		die("need at least two ranks");
+
+	instr_start(rank, nranks);
+	instr_nanos6_init();
+
+	/* Change the subsystem in a single thread, while the rest remain NULL.
+	 * This shouldn't cause a panic, as writting zero is ok for the other
+	 * sort outputs. */
+	if (rank == 0) {
+		instr_nanos6_worker_loop_enter();
+		instr_nanos6_worker_loop_exit();
+	}
+
+	instr_end();
+
+	return 0;
+}