diff --git a/ChangeLog b/ChangeLog
index 4b74e1fb39..12b8581b03 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Mon Jun 30 20:34:05 2008  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* string.c (str_buf_cat): check for self concatenation.
+
 Sun Jun 29 21:38:52 2008  Tanaka Akira  <akr@fsij.org>
 
 	* eval.c (rb_obj_respond_to): use RTEST to test the result of
diff --git a/string.c b/string.c
index 0fb0f3b4cf..cb619f86b3 100644
--- a/string.c
+++ b/string.c
@@ -693,9 +693,13 @@ str_buf_cat(str, ptr, len)
     const char *ptr;
     long len;
 {
-    long capa, total;
+    long capa, total, off = -1;;
 
     rb_str_modify(str);
+    if (ptr >= RSTRING(str)->ptr && ptr <= RSTRING(str)->ptr + RSTRING(str)->len) {
+        off = ptr - RSTRING(str)->ptr;
+    }
+    if (len == 0) return 0;
     if (FL_TEST(str, STR_ASSOC)) {
 	FL_UNSET(str, STR_ASSOC);
 	capa = RSTRING(str)->aux.capa = RSTRING(str)->len;
@@ -717,6 +721,9 @@ str_buf_cat(str, ptr, len)
 	}
 	RESIZE_CAPA(str, capa);
     }
+    if (off != -1) {
+        ptr = RSTRING(str)->ptr + off;
+    }
     memcpy(RSTRING(str)->ptr + RSTRING(str)->len, ptr, len);
     RSTRING(str)->len = total;
     RSTRING(str)->ptr[total] = '\0'; /* sentinel */
diff --git a/version.h b/version.h
index 5879c5a5b0..b822eae6d8 100644
--- a/version.h
+++ b/version.h
@@ -1,15 +1,15 @@
 #define RUBY_VERSION "1.8.6"
-#define RUBY_RELEASE_DATE "2008-06-29"
+#define RUBY_RELEASE_DATE "2008-06-30"
 #define RUBY_VERSION_CODE 186
-#define RUBY_RELEASE_CODE 20080629
-#define RUBY_PATCHLEVEL 255
+#define RUBY_RELEASE_CODE 20080630
+#define RUBY_PATCHLEVEL 256
 
 #define RUBY_VERSION_MAJOR 1
 #define RUBY_VERSION_MINOR 8
 #define RUBY_VERSION_TEENY 6
 #define RUBY_RELEASE_YEAR 2008
 #define RUBY_RELEASE_MONTH 6
-#define RUBY_RELEASE_DAY 29
+#define RUBY_RELEASE_DAY 30
 
 #ifdef RUBY_EXTERN
 RUBY_EXTERN const char ruby_version[];