diff --git a/ChangeLog b/ChangeLog
index 3fd581aa81..ffdf369015 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Sat Nov 21 18:48:35 2009  Tanaka Akira  <akr@fsij.org>
+
+	* vm_eval.c (rb_search_method_entry): show flags and klass value in
+	  not implemented error message.
+
 Sat Nov 21 16:38:50 2009  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* marshal.c (marshal_dump): use normal object as the buffer so
diff --git a/vm_eval.c b/vm_eval.c
index 49fe49dbba..d975809f31 100644
--- a/vm_eval.c
+++ b/vm_eval.c
@@ -336,22 +336,33 @@ rb_search_method_entry(VALUE recv, ID mid)
     VALUE klass = CLASS_OF(recv);
 
     if (!klass) {
-        if (!IMMEDIATE_P(recv) && RBASIC(recv)->flags != 0) {
+        if (IMMEDIATE_P(recv)) {
+            rb_raise(rb_eNotImpError,
+                     "method `%s' called on unexpected immediate object (%p)",
+                     rb_id2name(mid), (void *)recv);
+        }
+        if (RBASIC(recv)->flags == 0) {
+            rb_raise(rb_eNotImpError,
+                     "method `%s' called on terminated object"
+                     " (%p flags=0x%"PRIxVALUE" klass=0x%"PRIxVALUE")",
+                     rb_id2name(mid), (void *)recv,
+                     RBASIC(recv)->flags, RBASIC(recv)->klass);
+        }
+        else {
             int type = BUILTIN_TYPE(recv);
             const char *typestr = rb_type_str(type);
             if (typestr)
                 rb_raise(rb_eNotImpError,
-                         "method `%s' called on hidden %s object (%p)",
-                         rb_id2name(mid), typestr, (void *)recv);
+                         "method `%s' called on hidden %s object"
+                         " (%p flags=0x%"PRIxVALUE" klass=0x%"PRIxVALUE")",
+                         rb_id2name(mid), typestr, (void *)recv,
+                         RBASIC(recv)->flags, RBASIC(recv)->klass);
             else
                 rb_raise(rb_eNotImpError,
-                         "method `%s' called on hidden T_???" "(0x%02x) object (%p)",
-                         rb_id2name(mid), type, (void *)recv);
-        }
-        else {
-            rb_raise(rb_eNotImpError,
-                     "method `%s' called on terminated object (%p)",
-                     rb_id2name(mid), (void *)recv);
+                         "method `%s' called on hidden T_???" "(0x%02x) object"
+                         " (%p flags=0x%"PRIxVALUE" klass=0x%"PRIxVALUE")",
+                         rb_id2name(mid), type, (void *)recv,
+                         RBASIC(recv)->flags, RBASIC(recv)->klass);
         }
     }
     return rb_method_entry(klass, mid);