diff --git a/arch/xtensa/core/xtensa-asm2-util.S b/arch/xtensa/core/xtensa-asm2-util.S
index d46ea5ee3a7..0646c338672 100644
--- a/arch/xtensa/core/xtensa-asm2-util.S
+++ b/arch/xtensa/core/xtensa-asm2-util.S
@@ -248,14 +248,17 @@ xtensa_switch:
 
 #ifdef CONFIG_KERNEL_COHERENCE
 	/* Flush the stack.  The top of stack was stored for us in
-	 * EXCSAVE3 (FIXME: shouldn't be hardcoded!) by arch_cohere_stacks().
+	 * EXCSAVE3 (FIXME: shouldn't be hardcoded!) by
+	 * arch_cohere_stacks().  It can be NULL for a dummy thread.
 	 */
 	rsr.EXCSAVE3 a0
+	beqz a0, noflush
 	mov a3, a1
 flushloop:
 	dhwb a3, 0
 	addi a3, a3, XCHAL_DCACHE_LINESIZE
 	blt a3, a0, flushloop
+noflush:
 #endif
 
 	/* Restore the A3 argument we spilled earlier (via the base
diff --git a/arch/xtensa/include/kernel_arch_func.h b/arch/xtensa/include/kernel_arch_func.h
index 061b6a480eb..b69f951adce 100644
--- a/arch/xtensa/include/kernel_arch_func.h
+++ b/arch/xtensa/include/kernel_arch_func.h
@@ -111,7 +111,7 @@ static ALWAYS_INLINE void arch_cohere_stacks(struct k_thread *old_thread,
 	/* Dummy threads appear at system initialization, but don't
 	 * have stack_info data and will never be saved.  Ignore.
 	 */
-	if (!osz) {
+	if (old_thread->base.thread_state & _THREAD_DUMMY) {
 		return;
 	}