diff --git a/ChangeLog b/ChangeLog
index afd3d56373..32ed3e9787 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+Sat Jul 26 17:22:14 2014  URABE Shyouhei  <shyouhei@ruby-lang.org>
+
+	* ext/objspace/objspace_dump.c (dump_append): avoid fflush.
+
+	  because dump_append_string_value() iterates over each chars,
+	  fflush()-ing here effectively issues system calls on every single
+	  bytes exist in a ruby process.
+
 Sat Jul 26 16:55:18 2014  Eric Wong  <e@80x24.org>
 
 	* iseq.h (struct iseq_compile_data_storage): reduce overhead
diff --git a/ext/objspace/objspace_dump.c b/ext/objspace/objspace_dump.c
index 076d4fbaa1..e13cc39a6c 100644
--- a/ext/objspace/objspace_dump.c
+++ b/ext/objspace/objspace_dump.c
@@ -43,7 +43,6 @@ dump_append(struct dump_config *dc, const char *format, ...)
 
     if (dc->stream) {
 	vfprintf(dc->stream, format, vl);
-	fflush(dc->stream);
     }
     else if (dc->string)
 	rb_str_vcatf(dc->string, format, vl);