diff --git a/src/system/kernel/arch/arm/arch_thread.cpp b/src/system/kernel/arch/arm/arch_thread.cpp
index ff0ca0c36c..004ab26806 100644
--- a/src/system/kernel/arch/arm/arch_thread.cpp
+++ b/src/system/kernel/arch/arm/arch_thread.cpp
@@ -21,7 +21,6 @@
 #include <commpage.h>
 #include <kernel.h>
 #include <thread.h>
-#include <tls.h>
 #include <vm/vm_types.h>
 #include <vm/VMAddressSpace.h>
 #include <arch_vm.h>
@@ -117,20 +116,12 @@ arch_thread_init_kthread_stack(Thread* thread, void* _stack, void* _stackTop,
 status_t
 arch_thread_init_tls(Thread *thread)
 {
-	uint32 tls[TLS_FIRST_FREE_SLOT];
-
-	thread->user_local_storage = thread->user_stack_base
-		+ thread->user_stack_size;
-
-	// initialize default TLS fields
-	memset(tls, 0, sizeof(tls));
-	tls[TLS_BASE_ADDRESS_SLOT] = thread->user_local_storage;
-	tls[TLS_THREAD_ID_SLOT] = thread->id;
-	tls[TLS_USER_THREAD_SLOT] = (addr_t)thread->user_thread;
-
-	return user_memcpy((void *)thread->user_local_storage, tls, sizeof(tls));
+	thread->user_local_storage =
+		thread->user_stack_base + thread->user_stack_size;
+	return B_OK;
 }
 
+
 void
 arm_swap_pgdir(uint32_t pageDirectoryAddress)
 {
diff --git a/src/system/kernel/arch/riscv64/arch_thread.cpp b/src/system/kernel/arch/riscv64/arch_thread.cpp
index 21088c6eea..dd72296afa 100644
--- a/src/system/kernel/arch/riscv64/arch_thread.cpp
+++ b/src/system/kernel/arch/riscv64/arch_thread.cpp
@@ -13,7 +13,6 @@
 #include <kernel.h>
 #include <thread.h>
 #include <team.h>
-#include <tls.h>
 #include <vm/vm_types.h>
 #include <vm/VMAddressSpace.h>
 
@@ -80,18 +79,9 @@ arch_thread_init_kthread_stack(Thread* thread, void* _stack, void* _stackTop,
 status_t
 arch_thread_init_tls(Thread *thread)
 {
-	addr_t tls[TLS_FIRST_FREE_SLOT];
-
-	thread->user_local_storage = thread->user_stack_base
-		+ thread->user_stack_size;
-
-	// initialize default TLS fields
-	memset(tls, 0, sizeof(tls));
-	tls[TLS_BASE_ADDRESS_SLOT] = thread->user_local_storage;
-	tls[TLS_THREAD_ID_SLOT] = thread->id;
-	tls[TLS_USER_THREAD_SLOT] = (addr_t)thread->user_thread;
-
-	return user_memcpy((void*)thread->user_local_storage, tls, sizeof(tls));
+	thread->user_local_storage =
+		thread->user_stack_base + thread->user_stack_size;
+	return B_OK;
 }
 
 
diff --git a/src/system/kernel/arch/x86/arch_thread.cpp b/src/system/kernel/arch/x86/arch_thread.cpp
index f204693b3c..4af28e33a0 100644
--- a/src/system/kernel/arch/x86/arch_thread.cpp
+++ b/src/system/kernel/arch/x86/arch_thread.cpp
@@ -18,7 +18,6 @@
 #include <int.h>
 #include <team.h>
 #include <thread.h>
-#include <tls.h>
 #include <vm/vm_types.h>
 #include <vm/VMAddressSpace.h>
 
@@ -184,26 +183,12 @@ arch_team_init_team_struct(Team* p, bool kernel)
 }
 
 
-/*!	Initializes the user-space TLS local storage pointer in
-	the thread structure, and the reserved TLS slots.
-
-	Is called from _create_user_thread_kentry().
-*/
 status_t
-arch_thread_init_tls(Thread* thread)
+arch_thread_init_tls(Thread *thread)
 {
-	addr_t tls[TLS_FIRST_FREE_SLOT];
-
-	thread->user_local_storage = thread->user_stack_base
-		+ thread->user_stack_size;
-
-	// initialize default TLS fields
-	memset(tls, 0, sizeof(tls));
-	tls[TLS_BASE_ADDRESS_SLOT] = thread->user_local_storage;
-	tls[TLS_THREAD_ID_SLOT] = thread->id;
-	tls[TLS_USER_THREAD_SLOT] = (addr_t)thread->user_thread;
-
-	return user_memcpy((void*)thread->user_local_storage, tls, sizeof(tls));
+	thread->user_local_storage =
+		thread->user_stack_base + thread->user_stack_size;
+	return B_OK;
 }
 
 
diff --git a/src/system/kernel/thread.cpp b/src/system/kernel/thread.cpp
index c0851d3cb4..db0adcc4ee 100644
--- a/src/system/kernel/thread.cpp
+++ b/src/system/kernel/thread.cpp
@@ -659,9 +659,28 @@ enter_userspace(Thread* thread, UserThreadEntryArguments* args)
 	userThread->pending_signals = 0;
 	clear_ac();
 
-	if (args->forkArgs != NULL) {
-		// This is a fork()ed thread. Copy the fork args onto the stack and
-		// free them.
+	// initialize default TLS fields
+	addr_t tls[TLS_FIRST_FREE_SLOT];
+	memset(tls, 0, sizeof(tls));
+	tls[TLS_BASE_ADDRESS_SLOT] = thread->user_local_storage;
+	tls[TLS_THREAD_ID_SLOT] = thread->id;
+	tls[TLS_USER_THREAD_SLOT] = (addr_t)thread->user_thread;
+
+	if (args->forkArgs == NULL) {
+		if (user_memcpy((void*)thread->user_local_storage, tls, sizeof(tls)) != B_OK)
+			return B_BAD_ADDRESS;
+	} else {
+		// This is a fork()ed thread.
+
+		// Update select TLS values, do not clear the whole array.
+		set_ac();
+		addr_t* userTls = (addr_t*)thread->user_local_storage;
+		ASSERT(userTls[TLS_BASE_ADDRESS_SLOT] == thread->user_local_storage);
+		userTls[TLS_THREAD_ID_SLOT] = tls[TLS_THREAD_ID_SLOT];
+		userTls[TLS_USER_THREAD_SLOT] = tls[TLS_USER_THREAD_SLOT];
+		clear_ac();
+
+		// Copy the fork args onto the stack and free them.
 		arch_fork_arg archArgs = *args->forkArgs;
 		free(args->forkArgs);