diff --git a/defines.h b/defines.h
index b3371d4b2f..9e26a2522b 100644
--- a/defines.h
+++ b/defines.h
@@ -230,7 +230,7 @@ flush_register_windows(void)
 	;
 }
 #  define FLUSH_REGISTER_WINDOWS flush_register_windows()
-#elif defined(IA64)
+#elif defined(__ia64)
 void *rb_ia64_bsp(void);
 void rb_ia64_flushrs(void);
 #  define FLUSH_REGISTER_WINDOWS rb_ia64_flushrs()
diff --git a/ruby.h b/ruby.h
index c21661f1d2..50ebea3d29 100644
--- a/ruby.h
+++ b/ruby.h
@@ -583,7 +583,7 @@ NORETURN(void rb_throw(const char*,VALUE));
 
 VALUE rb_require(const char*);
 
-#ifdef IA64
+#ifdef __ia64
 void ruby_init_stack(VALUE*, void*);
 #define RUBY_INIT_STACK \
     VALUE variable_in_this_stack_frame; \