diff --git a/arch/x86/core/userspace.c b/arch/x86/core/userspace.c
index 4f82d6e466d..3df7087afd4 100644
--- a/arch/x86/core/userspace.c
+++ b/arch/x86/core/userspace.c
@@ -110,8 +110,11 @@ void *z_x86_userspace_prepare_thread(struct k_thread *thread)
 FUNC_NORETURN void arch_user_mode_enter(k_thread_entry_t user_entry,
 					void *p1, void *p2, void *p3)
 {
+	k_spinlock_key_t key;
+
 	z_x86_thread_pt_init(_current);
 
+	key = k_spin_lock(&z_mem_domain_lock);
 	/* Apply memory domain configuration, if assigned. Threads that
 	 * started in user mode already had this done via z_setup_new_thread()
 	 */
@@ -119,6 +122,7 @@ FUNC_NORETURN void arch_user_mode_enter(k_thread_entry_t user_entry,
 		z_x86_apply_mem_domain(_current,
 				       _current->mem_domain_info.mem_domain);
 	}
+	k_spin_unlock(&z_mem_domain_lock, key);
 
 #ifndef CONFIG_X86_KPTI
 	/* We're synchronously dropping into user mode from a thread that
diff --git a/arch/x86/include/x86_mmu.h b/arch/x86/include/x86_mmu.h
index 158c765ba51..6a81d0c5be4 100644
--- a/arch/x86/include/x86_mmu.h
+++ b/arch/x86/include/x86_mmu.h
@@ -119,7 +119,10 @@ extern uint8_t z_shared_kernel_page_start;
 /* Set up per-thread page tables just prior to entering user mode */
 void z_x86_thread_pt_init(struct k_thread *thread);
 
-/* Apply a memory domain policy to a set of thread page tables */
+/* Apply a memory domain policy to a set of thread page tables.
+ *
+ * Must be called with z_mem_domain_lock held.
+ */
 void z_x86_apply_mem_domain(struct k_thread *thread,
 			    struct k_mem_domain *mem_domain);
 #endif /* CONFIG_USERSPACE */