diff --git a/ChangeLog b/ChangeLog
index 4f0f7c9724..c15ffe171e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Wed Dec  8 14:31:36 2004  Yukihiro Matsumoto  <matz@ruby-lang.org>
+
+	* sprintf.c (rb_f_sprintf): [ruby-dev:25104]
+
 Wed Dec  8 13:49:46 2004  NAKAMURA Usaku  <usa@ruby-lang.org>
 
 	* win32/win32.c (rb_w32_pipe_exec): must close original handle
diff --git a/sprintf.c b/sprintf.c
index 16f9c35a3e..97c392816b 100644
--- a/sprintf.c
+++ b/sprintf.c
@@ -249,6 +249,7 @@ rb_f_sprintf(argc, argv)
     fmt = GETNTHARG(0);
     if (OBJ_TAINTED(fmt)) tainted = 1;
     StringValue(fmt);
+    fmt = rb_str_new4(fmt);
     p = RSTRING(fmt)->ptr;
     end = p + RSTRING(fmt)->len;
     blen = 0;