diff --git a/include/app_memory/mem_domain.h b/include/app_memory/mem_domain.h
index c1946bca75e..845c8154d67 100644
--- a/include/app_memory/mem_domain.h
+++ b/include/app_memory/mem_domain.h
@@ -92,6 +92,18 @@ struct k_mem_domain {
 	struct arch_mem_domain arch;
 #endif /* CONFIG_ARCH_MEM_DOMAIN_DATA */
 };
+
+/**
+ * Default memory domain
+ *
+ * All threads are a member of some memory domain, even if running in
+ * supervisor mode. Threads belong to this default memory domain if they
+ * haven't been added to or inherited membership from some other domain.
+ *
+ * This memory domain has the z_libc_partition partition for the C library
+ * added to it if exists.
+ */
+extern struct k_mem_domain k_mem_domain_default;
 #else
 /* To support use of IS_ENABLED for the APIs below */
 struct k_mem_domain;
@@ -164,7 +176,8 @@ extern void k_mem_domain_remove_partition(struct k_mem_domain *domain,
 /**
  * @brief Add a thread into a memory domain.
  *
- * Add a thread into a memory domain.
+ * Add a thread into a memory domain. It will be removed from whatever
+ * memory domain it previously belonged to.
  *
  * @param domain The memory domain that the thread is going to be added into.
  * @param thread ID of thread going to be added into the memory domain.
diff --git a/kernel/include/kswap.h b/kernel/include/kswap.h
index 7a0b42f17fb..8bf5721eb36 100644
--- a/kernel/include/kswap.h
+++ b/kernel/include/kswap.h
@@ -197,7 +197,7 @@ static inline void z_dummy_thread_init(struct k_thread *dummy_thread)
 	dummy_thread->stack_info.size = 0U;
 #endif
 #ifdef CONFIG_USERSPACE
-	dummy_thread->mem_domain_info.mem_domain = 0;
+	dummy_thread->mem_domain_info.mem_domain = &k_mem_domain_default;
 #endif
 
 	_current_cpu->current = dummy_thread;
diff --git a/kernel/mem_domain.c b/kernel/mem_domain.c
index 1589ad4f12e..97f3e10532f 100644
--- a/kernel/mem_domain.c
+++ b/kernel/mem_domain.c
@@ -11,6 +11,7 @@
 #include <sys/__assert.h>
 #include <stdbool.h>
 #include <spinlock.h>
+#include <sys/libc-hooks.h>
 
 #define LOG_LEVEL CONFIG_KERNEL_LOG_LEVEL
 #include <logging/log.h>
@@ -19,6 +20,8 @@ LOG_MODULE_DECLARE(os);
 static struct k_spinlock lock;
 static uint8_t max_partitions;
 
+struct k_mem_domain k_mem_domain_default;
+
 #if __ASSERT_ON
 static bool check_add_partition(struct k_mem_domain *domain,
 				struct k_mem_partition *part)
@@ -225,12 +228,12 @@ void k_mem_domain_add_thread(struct k_mem_domain *domain, k_tid_t thread)
 
 	__ASSERT_NO_MSG(domain != NULL);
 	__ASSERT_NO_MSG(thread != NULL);
-	__ASSERT(thread->mem_domain_info.mem_domain == NULL,
-		 "thread %p belongs to a different memory domain %p",
-		 thread, thread->mem_domain_info.mem_domain);
 
 	key = k_spin_lock(&lock);
-
+	if (thread->mem_domain_info.mem_domain != NULL) {
+		sys_dlist_remove(&thread->mem_domain_info.mem_domain_q_node);
+		arch_mem_domain_thread_remove(thread);
+	}
 	sys_dlist_append(&domain->mem_domain_q,
 			 &thread->mem_domain_info.mem_domain_q_node);
 	thread->mem_domain_info.mem_domain = domain;
@@ -242,18 +245,7 @@ void k_mem_domain_add_thread(struct k_mem_domain *domain, k_tid_t thread)
 
 void k_mem_domain_remove_thread(k_tid_t thread)
 {
-	k_spinlock_key_t key;
-
-	__ASSERT_NO_MSG(thread != NULL);
-	__ASSERT(thread->mem_domain_info.mem_domain != NULL,
-		 "thread does not belong to a memory domain");
-
-	key = k_spin_lock(&lock);
-	arch_mem_domain_thread_remove(thread);
-
-	sys_dlist_remove(&thread->mem_domain_info.mem_domain_q_node);
-	thread->mem_domain_info.mem_domain = NULL;
-	k_spin_unlock(&lock, key);
+	k_mem_domain_add_thread(&k_mem_domain_default, thread);
 }
 
 static int init_mem_domain_module(struct device *arg)
@@ -268,6 +260,11 @@ static int init_mem_domain_module(struct device *arg)
 	 */
 	__ASSERT(max_partitions <= CONFIG_MAX_DOMAIN_PARTITIONS, "");
 
+	k_mem_domain_init(&k_mem_domain_default, 0, NULL);
+#ifdef Z_LIBC_PARTITION_EXISTS
+	k_mem_domain_add_partition(&k_mem_domain_default, &z_libc_partition);
+#endif /* Z_LIBC_PARTITION_EXISTS */
+
 	return 0;
 }
 
diff --git a/kernel/thread.c b/kernel/thread.c
index e8050b23524..1bbffd8dd19 100644
--- a/kernel/thread.c
+++ b/kernel/thread.c
@@ -537,7 +537,6 @@ char *z_setup_new_thread(struct k_thread *new_thread,
 	z_object_init(new_thread);
 	z_object_init(stack);
 	new_thread->stack_obj = stack;
-	new_thread->mem_domain_info.mem_domain = NULL;
 	new_thread->syscall_frame = NULL;
 
 	/* Any given thread has access to itself */
@@ -601,10 +600,9 @@ char *z_setup_new_thread(struct k_thread *new_thread,
 #endif
 #ifdef CONFIG_USERSPACE
 	/* New threads inherit any memory domain membership by the parent */
-	if (_current->mem_domain_info.mem_domain != NULL) {
-		k_mem_domain_add_thread(_current->mem_domain_info.mem_domain,
-					new_thread);
-	}
+	new_thread->mem_domain_info.mem_domain = NULL;
+	k_mem_domain_add_thread(_current->mem_domain_info.mem_domain,
+				new_thread);
 
 	if ((options & K_INHERIT_PERMS) != 0U) {
 		z_thread_perms_inherit(_current, new_thread);