diff --git a/ChangeLog b/ChangeLog
index 27f309b8a1..a77b678b3f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Mon Jan 24 21:28:34 2011  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
+
+	* object.c (rb_str_to_dbl): use ALLOC_N instead ALLOCA_N because
+	  ALLOC_N may cause stack overflow.
+
 Mon Jan 24 21:04:45 2011  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* error.c (rb_invalid_str): prevent intermediate variable from GC.
diff --git a/object.c b/object.c
index 75192c1504..97989fd82a 100644
--- a/object.c
+++ b/object.c
@@ -2245,6 +2245,8 @@ rb_str_to_dbl(VALUE str, int badcheck)
 {
     char *s;
     long len;
+    double ret;
+    char *alloced = NULL;
 
     StringValue(str);
     s = RSTRING_PTR(str);
@@ -2254,14 +2256,16 @@ rb_str_to_dbl(VALUE str, int badcheck)
 	    rb_raise(rb_eArgError, "string for Float contains null byte");
 	}
 	if (s[len]) {		/* no sentinel somehow */
-	    char *p = ALLOCA_N(char, len+1);
-
+	    char *p = alloced = ALLOC_N(char, len+1);
 	    MEMCPY(p, s, char, len);
 	    p[len] = '\0';
 	    s = p;
 	}
     }
-    return rb_cstr_to_dbl(s, badcheck);
+    ret = rb_cstr_to_dbl(s, badcheck);
+    if (alloced)
+	xfree(alloced);
+    return ret;
 }
 
 VALUE