diff --git a/ChangeLog b/ChangeLog
index a3fc2a7749..90474f1daf 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Fri Jun  7 13:25:27 2013  NARUSE, Yui  <naruse@ruby-lang.org>
+
+	* ext/json/fbuffer/fbuffer.h (fbuffer_append_str): change the place of
+	  RB_GC_GUARD. it should be after the object is used.
+
 Fri Jun  7 13:22:43 2013  NARUSE, Yui  <naruse@ruby-lang.org>
 
 	* gc.c (before_gc_sweep): noinline can also avoid the segv instead of
diff --git a/ext/json/fbuffer/fbuffer.h b/ext/json/fbuffer/fbuffer.h
index af74187566..24bb088521 100644
--- a/ext/json/fbuffer/fbuffer.h
+++ b/ext/json/fbuffer/fbuffer.h
@@ -117,9 +117,9 @@ static void fbuffer_append_str(FBuffer *fb, VALUE str)
     const char *newstr = StringValuePtr(str);
     unsigned long len = RSTRING_LEN(str);
 
-    RB_GC_GUARD(str);
-
     fbuffer_append(fb, newstr, len);
+
+    RB_GC_GUARD(str);
 }
 #endif