diff --git a/ChangeLog b/ChangeLog
index 9ef9d4b2cb..02acc2ebba 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Thu Jul 30 21:48:56 2009  Yusuke Endoh  <mame@tsg.ne.jp>
+
+	* random.c (init_genrand): ensure invariant of mt->next and mt->left.
+	  mt->next should always equal mt->state + N + 1 - mt->left.
+	  In fact, 'r = Random.new(0); r == r.dup' has returned false.
+
 Thu Jul 30 21:43:41 2009  Yusuke Endoh  <mame@tsg.ne.jp>
 
 	* random.c (random_bytes): use NUM2LONG instead of FIX2LONG because
diff --git a/random.c b/random.c
index bfdfaf6f3c..7aefb4d4fb 100644
--- a/random.c
+++ b/random.c
@@ -98,7 +98,7 @@ init_genrand(struct MT *mt, unsigned int s)
         mt->state[j] &= 0xffffffff;  /* for >32 bit machines */
     }
     mt->left = 1;
-    mt->next = mt->state + N - 1;
+    mt->next = mt->state + N;
 }
 
 /* initialize by an array with array-length */