diff --git a/ChangeLog b/ChangeLog
index 01f47dcb28..e216c586ed 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Mon Jul 25 16:59:00 2016  Koichi Sasada  <ko1@atdot.net>
+
+	* debug.c (ruby_debug_printf): use rb_raw_obj_info()
+	  instead of rb_inspect() because it is more robust way
+	  to see object internal.
+
 Sun Jul 24 16:33:13 2016  Martin Duerst  <duerst@it.aoyama.ac.jp>
 
 	* regenc.h/c, include/ruby/oniguruma.h, enc/ascii.c, big5.c, cp949.c,
diff --git a/debug.c b/debug.c
index a600259818..8a5e69bbf5 100644
--- a/debug.c
+++ b/debug.c
@@ -59,14 +59,16 @@ ruby_debug_printf(const char *format, ...)
     va_end(ap);
 }
 
+#include "gc.h"
+
 VALUE
 ruby_debug_print_value(int level, int debug_level, const char *header, VALUE obj)
 {
     if (level < debug_level) {
-	VALUE str;
-	str = rb_inspect(obj);
-	fprintf(stderr, "DBG> %s: %s\n", header,
-		obj == (VALUE)(SIGNED_VALUE)-1 ? "" : StringValueCStr(str));
+	char buff[0x100];
+	rb_raw_obj_info(buff, 0x100, obj);
+
+	fprintf(stderr, "DBG> %s: %s\n", header, buff);
 	fflush(stderr);
     }
     return obj;