diff --git a/ChangeLog b/ChangeLog
index e9f66dd3ce..7c21bc9da4 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Sun Dec 20 11:01:57 2015  Koichi Sasada  <ko1@atdot.net>
+
+	* proc.c (rb_mod_define_method): fix notation.
+
 Sun Dec 20 10:54:15 2015  Koichi Sasada  <ko1@atdot.net>
 
 	* proc.c (proc_new): fix notation.
diff --git a/proc.c b/proc.c
index 79a78292f7..cd083ec2bf 100644
--- a/proc.c
+++ b/proc.c
@@ -1782,8 +1782,14 @@ rb_mod_define_method(int argc, VALUE *argv, VALUE mod)
     }
     else {
 	body = argv[1];
-	is_method = rb_obj_is_method(body) != Qfalse;
-	if (!is_method && !rb_obj_is_proc(body)) {
+
+	if (rb_obj_is_method(body)) {
+	    is_method = TRUE;
+	}
+	else if (rb_obj_is_proc(body)) {
+	    is_method = FALSE;
+	}
+	else {
 	    rb_raise(rb_eTypeError,
 		     "wrong argument type %s (expected Proc/Method)",
 		     rb_obj_classname(body));