diff --git a/include/ruby/defines.h b/include/ruby/defines.h
index 2ef26d0da8..de0883d2c9 100644
--- a/include/ruby/defines.h
+++ b/include/ruby/defines.h
@@ -198,7 +198,7 @@ void xfree(void*);
 #endif
 
 #if defined(__sparc)
-void rb_sparc_flush_register_windows();
+void rb_sparc_flush_register_windows(void);
 #  define FLUSH_REGISTER_WINDOWS rb_sparc_flush_register_windows()
 #elif defined(__ia64)
 void *rb_ia64_bsp(void);
diff --git a/sparc.c b/sparc.c
index b764e900d7..2d368dfe5b 100644
--- a/sparc.c
+++ b/sparc.c
@@ -9,7 +9,7 @@
 
  See http://redmine.ruby-lang.org/issues/5244 for discussion.
 *********************************************************************/
-void rb_sparc_flush_register_windows()
+void rb_sparc_flush_register_windows(void)
 {
     asm
 #ifdef __GNUC__