diff --git a/ChangeLog b/ChangeLog
index d5586df802..32d53da55c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Sat Nov 15 22:16:42 2003  GOTOU Yuuzou  <gotoyuzo@notwork.org>
+
+	* /ext/openssl/ossl_x509ext.c (ossl_x509extfactory_create_ext):
+	  refine error message.
+
 Sat Nov 15 10:05:40 2003  Tanaka Akira  <akr@m17n.org>
 
 	* lib/open-uri.rb (OpenURI.open_loop, OpenURI::HTTP#proxy_open): 
diff --git a/ext/openssl/ossl_x509ext.c b/ext/openssl/ossl_x509ext.c
index d9ec846ac1..f0ce068d6b 100644
--- a/ext/openssl/ossl_x509ext.c
+++ b/ext/openssl/ossl_x509ext.c
@@ -223,11 +223,14 @@ ossl_x509extfactory_create_ext(int argc, VALUE *argv, VALUE self)
 
     nid = OBJ_ln2nid(RSTRING(oid)->ptr);
     if(!nid) nid = OBJ_sn2nid(RSTRING(oid)->ptr);
-    if(!nid) ossl_raise(eX509ExtError, NULL);
+    if(!nid) ossl_raise(eX509ExtError, "unknown OID `%s'", RSTRING(oid)->ptr);
     valstr = rb_str_new2(RTEST(critical) ? "critical," : "");
     rb_str_append(valstr, value);
     ext = X509V3_EXT_conf_nid(NULL, ctx, nid, RSTRING(valstr)->ptr);
-    if (!ext) ossl_raise(eX509ExtError, NULL);
+    if (!ext){
+	ossl_raise(eX509ExtError, "%s = %s",
+		   RSTRING(oid)->ptr, RSTRING(value)->ptr);
+    }
     WrapX509Ext(cX509Ext, obj, ext);
 
     return obj;