diff --git a/ChangeLog b/ChangeLog
index 6bb07bb370..a2278ec6b1 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Thu Aug 23 20:34:32 2012  NAKAMURA Usaku  <usa@ruby-lang.org>
+
+	* class.c (singleton_class_of): flonum can't have singleton class.
+
+	* vm.c (vm_define_method): flonum can't have singleton method.
+
 Thu Aug 23 19:18:33 2012  NAKAMURA Usaku  <usa@ruby-lang.org>
 
 	* common.mk (win32/*): macro RUBY_H_INCLUDES is not defined there,
diff --git a/class.c b/class.c
index 2ee5b8867a..1d871fb7ee 100644
--- a/class.c
+++ b/class.c
@@ -1315,7 +1315,7 @@ singleton_class_of(VALUE obj)
 {
     VALUE klass;
 
-    if (FIXNUM_P(obj) || SYMBOL_P(obj)) {
+    if (FIXNUM_P(obj) || FLONUM_P(obj) || SYMBOL_P(obj)) {
 	rb_raise(rb_eTypeError, "can't define singleton");
     }
     if (SPECIAL_CONST_P(obj)) {
diff --git a/vm.c b/vm.c
index ed4d31e95f..55ccfe7939 100644
--- a/vm.c
+++ b/vm.c
@@ -1857,7 +1857,7 @@ vm_define_method(rb_thread_t *th, VALUE obj, ID id, VALUE iseqval,
     }
 
     if (is_singleton) {
-	if (FIXNUM_P(obj) || SYMBOL_P(obj)) {
+	if (FIXNUM_P(obj) || FLONUM_P(obj) || SYMBOL_P(obj)) {
 	    rb_raise(rb_eTypeError,
 		     "can't define singleton method \"%s\" for %s",
 		     rb_id2name(id), rb_obj_classname(obj));