diff --git a/arch/sim/src/sim/up_vfork.c b/arch/sim/src/sim/up_vfork.c
index 7560be60c79..af8820716ae 100644
--- a/arch/sim/src/sim/up_vfork.c
+++ b/arch/sim/src/sim/up_vfork.c
@@ -89,6 +89,8 @@ pid_t up_vfork(const xcpt_reg_t *context)
 {
   struct tcb_s *parent = this_task();
   struct task_tcb_s *child;
+  unsigned char *pout;
+  unsigned char *pin;
   xcpt_reg_t newsp;
   xcpt_reg_t newfp;
   xcpt_reg_t newtop;
@@ -133,7 +135,9 @@ pid_t up_vfork(const xcpt_reg_t *context)
   newtop = (xcpt_reg_t)child->cmn.stack_base_ptr +
                        child->cmn.adj_stack_size;
   newsp = newtop - stackutil;
-  memcpy((void *)newsp, (const void *)context[JB_SP], stackutil);
+  pout = (unsigned char *)newsp;
+  pin  = (unsigned char *)context[JB_SP];
+  while (stackutil-- > 0) *pout++ = *pin++;
 
   /* Was there a frame pointer in place before? */