diff --git a/arch/um/drivers/xterm.c b/arch/um/drivers/xterm.c
index 386f8b952982e4317f5254e4016a2e7ba18597d1..850221d9b4c953306d87817bfd455551dc4aee67 100644
--- a/arch/um/drivers/xterm.c
+++ b/arch/um/drivers/xterm.c
@@ -136,8 +136,6 @@ int xterm_open(int input, int output, int primary, void *d,
 		return(pid);
 	}
 
-	if(data->stack == 0) free_stack(stack, 0);
-
 	if (data->direct_rcv) {
 		new = os_rcv_fd(fd, &data->helper_pid);
 	} else {
diff --git a/arch/um/os-Linux/helper.c b/arch/um/os-Linux/helper.c
index 8a78bf03b468c4e83a4d1ae039146b029d379af9..d13299cfa31878e6b725e3ad86d5ac9fdd50922d 100644
--- a/arch/um/os-Linux/helper.c
+++ b/arch/um/os-Linux/helper.c
@@ -50,7 +50,8 @@ static int helper_child(void *arg)
 }
 
 /* Returns either the pid of the child process we run or -E* on failure.
- * XXX The alloc_stack here breaks if this is called in the tracing thread */
+ * XXX The alloc_stack here breaks if this is called in the tracing thread, so
+ * we need to receive a preallocated stack (a local buffer is ok). */
 int run_helper(void (*pre_exec)(void *), void *pre_data, char **argv,
 	       unsigned long *stack_out)
 {
@@ -113,10 +114,8 @@ int run_helper(void (*pre_exec)(void *), void *pre_data, char **argv,
 		close(fds[1]);
 	close(fds[0]);
 out_free:
-	if (stack_out == NULL)
+	if ((stack_out == NULL) || (*stack_out == 0))
 		free_stack(stack, 0);
-	else
-		*stack_out = stack;
 	return ret;
 }