diff --git a/ChangeLog b/ChangeLog
index a567c43c9e..ecd342eb2b 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Fri Jun 20 18:23:09 2008  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* string.c (rb_str_buf_append): should infect.
+
 Fri Jun 20 15:51:18 2008  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* array.c (rb_ary_store, rb_ary_splice): not depend on unspecified
diff --git a/string.c b/string.c
index 4f27d431ff..f0cea48267 100644
--- a/string.c
+++ b/string.c
@@ -775,7 +775,9 @@ VALUE
 rb_str_buf_append(str, str2)
     VALUE str, str2;
 {
-    return str_buf_cat(str, RSTRING(str2)->ptr, RSTRING(str2)->len);
+    str_buf_cat(str, RSTRING(str2)->ptr, RSTRING(str2)->len);
+    OBJ_INFECT(str, str2);
+    return str;
 }
 
 VALUE
diff --git a/version.h b/version.h
index 9d574445cd..c0b484a8f8 100644
--- a/version.h
+++ b/version.h
@@ -2,7 +2,7 @@
 #define RUBY_RELEASE_DATE "2008-06-20"
 #define RUBY_VERSION_CODE 185
 #define RUBY_RELEASE_CODE 20080620
-#define RUBY_PATCHLEVEL 230
+#define RUBY_PATCHLEVEL 231
 
 #define RUBY_VERSION_MAJOR 1
 #define RUBY_VERSION_MINOR 8