diff --git a/ChangeLog b/ChangeLog
index dfa5dae248..8ab825e7f7 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Fri Jun 27 00:00:14 2008  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* ruby.c (set_arg0, ruby_prog_init): freeze $0.  a patch from Keita
+	  Yamaguchi <keita.yamaguchi at gmail.com>.
+
 Thu Jun 26 22:07:54 2008  Tanaka Akira  <akr@fsij.org>
 
 	* process.c: include sys/resource.h if HAVE_SYS_RESOURCE_H is defined.
diff --git a/ruby.c b/ruby.c
index 9c011ce1f2..0f00a2751a 100644
--- a/ruby.c
+++ b/ruby.c
@@ -1044,6 +1044,7 @@ set_arg0(val, id)
     VALUE val;
     ID id;
 {
+    VALUE progname;
     char *s;
     long i;
 #if !defined(PSTAT_SETCMD) && !defined(HAVE_SETPROCTITLE)
@@ -1068,10 +1069,10 @@ set_arg0(val, id)
 	j.pst_command = s;
 	pstat(PSTAT_SETCMD, j, i, 0, 0);
     }
-    rb_progname = rb_tainted_str_new(s, i);
+    progname = rb_tainted_str_new(s, i);
 #elif defined(HAVE_SETPROCTITLE)
     setproctitle("%.*s", (int)i, s);
-    rb_progname = rb_tainted_str_new(s, i);
+    progname = rb_tainted_str_new(s, i);
 #else
     if (len == 0) {
 	char *s = origargv[0];
@@ -1106,8 +1107,9 @@ set_arg0(val, id)
     if (++i < len) memset(s + 1, ' ', len - i);
     for (i = 1; i < origargc; i++)
 	origargv[i] = s;
-    rb_progname = rb_tainted_str_new2(origargv[0]);
+    progname = rb_tainted_str_new2(origargv[0]);
 #endif
+    rb_progname = rb_obj_freeze(progname);
 }
 
 void
@@ -1115,7 +1117,7 @@ ruby_script(name)
     const char *name;
 {
     if (name) {
-	rb_progname = rb_tainted_str_new2(name);
+	rb_progname = rb_obj_freeze(rb_tainted_str_new2(name));
 	ruby_sourcefile = rb_source_filename(name);
     }
 }