diff --git a/arch/arm64/include/irq.h b/arch/arm64/include/irq.h
index 933ded64667..debac2522a0 100644
--- a/arch/arm64/include/irq.h
+++ b/arch/arm64/include/irq.h
@@ -280,6 +280,9 @@ struct xcptcontext
   /* task stack reg context */
 
   uint64_t *regs;
+#ifndef CONFIG_BUILD_FLAT
+  uint64_t *initregs;
+#endif
 
   /* task context, for signal process */
 
diff --git a/arch/arm64/src/common/arm64_initialstate.c b/arch/arm64/src/common/arm64_initialstate.c
index b61f01b3b26..6e10432a436 100644
--- a/arch/arm64/src/common/arm64_initialstate.c
+++ b/arch/arm64/src/common/arm64_initialstate.c
@@ -108,6 +108,10 @@ void arm64_new_task(struct tcb_s * tcb)
   pinitctx->tpidr_el1 = (uint64_t)tcb;
 
   tcb->xcp.regs       = (uint64_t *)pinitctx;
+
+#ifndef CONFIG_BUILD_FLAT
+  tcb->xcp.initregs   = tcb->xcp.regs;
+#endif
 }
 
 /****************************************************************************
diff --git a/arch/arm64/src/common/arm64_pthread_start.c b/arch/arm64/src/common/arm64_pthread_start.c
index f063c9b2848..db80db228b6 100644
--- a/arch/arm64/src/common/arm64_pthread_start.c
+++ b/arch/arm64/src/common/arm64_pthread_start.c
@@ -68,8 +68,11 @@
 void up_pthread_start(pthread_trampoline_t startup,
                       pthread_startroutine_t entrypt, pthread_addr_t arg)
 {
-  struct tcb_s *tcb = this_task();
-  uint64_t spsr;
+  uint64_t *regs = this_task()->xcp.initregs;
+
+  /* This must be performed atomically, the C-section ends upon user entry */
+
+  enter_critical_section();
 
   /* Set up to enter the user-space pthread start-up function in
    * unprivileged mode. We need:
@@ -80,11 +83,10 @@ void up_pthread_start(pthread_trampoline_t startup,
    *   SPSR = user mode
    */
 
-  tcb->xcp.regs[REG_ELR]  = (uint64_t)startup;
-  tcb->xcp.regs[REG_X0]   = (uint64_t)entrypt;
-  tcb->xcp.regs[REG_X1]   = (uint64_t)arg;
-  spsr                    = tcb->xcp.regs[REG_SPSR] & ~SPSR_MODE_MASK;
-  tcb->xcp.regs[REG_SPSR] = spsr | SPSR_MODE_EL0T;
+  regs[REG_ELR]  = (uint64_t)startup;
+  regs[REG_X0]   = (uint64_t)entrypt;
+  regs[REG_X1]   = (uint64_t)arg;
+  regs[REG_SPSR] = (regs[REG_SPSR] & ~SPSR_MODE_MASK) | SPSR_MODE_EL0T;
 
   /* Fully unwind the kernel stack and drop to user space */
 
@@ -94,8 +96,8 @@ void up_pthread_start(pthread_trampoline_t startup,
     "mov sp, x0\n" /* Stack pointer = context */
     "b arm64_exit_exception\n"
     :
-    : "r" (tcb->xcp.regs)
-    : "memory"
+    : "r" (regs)
+    : "x0", "memory"
   );
 
   PANIC();
diff --git a/arch/arm64/src/common/arm64_task_start.c b/arch/arm64/src/common/arm64_task_start.c
index fd91e7b378e..5e3501eee6f 100644
--- a/arch/arm64/src/common/arm64_task_start.c
+++ b/arch/arm64/src/common/arm64_task_start.c
@@ -65,8 +65,11 @@
 
 void up_task_start(main_t taskentry, int argc, char *argv[])
 {
-  struct tcb_s *tcb = this_task();
-  uint64_t spsr;
+  uint64_t *regs = this_task()->xcp.initregs;
+
+  /* This must be performed atomically, the C-section ends upon user entry */
+
+  enter_critical_section();
 
   /* Set up to return to the user-space _start function in
    * unprivileged mode.  We need:
@@ -77,11 +80,10 @@ void up_task_start(main_t taskentry, int argc, char *argv[])
    *   SPSR = user mode
    */
 
-  tcb->xcp.regs[REG_ELR]  = (uint64_t)taskentry;
-  tcb->xcp.regs[REG_X0]   = (uint64_t)argc;
-  tcb->xcp.regs[REG_X1]   = (uint64_t)argv;
-  spsr                    = tcb->xcp.regs[REG_SPSR] & ~SPSR_MODE_MASK;
-  tcb->xcp.regs[REG_SPSR] = spsr | SPSR_MODE_EL0T;
+  regs[REG_ELR]  = (uint64_t)taskentry;
+  regs[REG_X0]   = (uint64_t)argc;
+  regs[REG_X1]   = (uint64_t)argv;
+  regs[REG_SPSR] = (regs[REG_SPSR] & ~SPSR_MODE_MASK) | SPSR_MODE_EL0T;
 
   /* Fully unwind the kernel stack and drop to user space */
 
@@ -91,8 +93,8 @@ void up_task_start(main_t taskentry, int argc, char *argv[])
     "mov sp, x0\n" /* Stack pointer = context */
     "b arm64_exit_exception\n"
     :
-    : "r" (tcb->xcp.regs)
-    : "memory"
+    : "r" (regs)
+    : "x0", "memory"
   );
 
   PANIC();