diff --git a/thread_pthread.c b/thread_pthread.c
index f652429637..18170c8e16 100644
--- a/thread_pthread.c
+++ b/thread_pthread.c
@@ -740,6 +740,12 @@ ruby_init_stack(volatile VALUE *addr
     )
 {
     native_main_thread.id = pthread_self();
+#ifdef __ia64
+    if (!native_main_thread.register_stack_start ||
+        (VALUE*)bsp < native_main_thread.register_stack_start) {
+        native_main_thread.register_stack_start = (VALUE*)bsp;
+    }
+#endif
 #if MAINSTACKADDR_AVAILABLE
     if (native_main_thread.stack_maxsize) return;
     {
@@ -762,12 +768,6 @@ ruby_init_stack(volatile VALUE *addr
                     native_main_thread.stack_start < addr)) {
         native_main_thread.stack_start = (VALUE *)addr;
     }
-#endif
-#ifdef __ia64
-    if (!native_main_thread.register_stack_start ||
-        (VALUE*)bsp < native_main_thread.register_stack_start) {
-        native_main_thread.register_stack_start = (VALUE*)bsp;
-    }
 #endif
     {
 #if defined(HAVE_GETRLIMIT)