diff --git a/ChangeLog b/ChangeLog
index 7c0f6b8a05..baa929f68a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Mon Jul 22 18:01:33 2013  Masaki Matsushita  <glass.saga@gmail.com>
+
+	* string.c (rb_str_enumerate_chars): specify array capa.
+
 Mon Jul 22 17:24:14 2013  Masaki Matsushita  <glass.saga@gmail.com>
 
 	* string.c (rb_str_each_char_size): performance improvement by
diff --git a/string.c b/string.c
index e5d04cddc6..a4c76d4f7b 100644
--- a/string.c
+++ b/string.c
@@ -6518,7 +6518,7 @@ rb_str_enumerate_chars(VALUE str, int wantarray)
 	if (wantarray) {
 #if STRING_ENUMERATORS_WANTARRAY
 	    rb_warn("given block not used");
-	    ary = rb_ary_new();
+	    ary = rb_ary_new_capa(rb_str_strlen(str));
 #else
 	    rb_warning("passing a block to String#chars is deprecated");
 	    wantarray = 0;
@@ -6527,7 +6527,7 @@ rb_str_enumerate_chars(VALUE str, int wantarray)
     }
     else {
 	if (wantarray)
-	    ary = rb_ary_new();
+	    ary = rb_ary_new_capa(rb_str_strlen(str));
 	else
 	    RETURN_SIZED_ENUMERATOR(str, 0, 0, rb_str_each_char_size);
     }