diff --git a/ChangeLog b/ChangeLog
index 18cdb865c0..dd4c3d35d1 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Wed Jan 27 22:48:40 2010  Yusuke Endoh  <mame@tsg.ne.jp>
+
+	* lib/matrix.rb (determinant): fix name error.
+
 Wed Jan 27 22:26:25 2010  Yusuke Endoh  <mame@tsg.ne.jp>
 
 	* vm_eval.c (rb_backtrace): "circular require" warning was output to
diff --git a/lib/matrix.rb b/lib/matrix.rb
index c7ae64923f..358ac04416 100644
--- a/lib/matrix.rb
+++ b/lib/matrix.rb
@@ -681,8 +681,8 @@ class Matrix
         i = (k+1 ... size).find {|ii|
           a[ii][k] != 0
         }
-        return 0 if ii.nil?
-        a[ii], a[k] = a[k], a[ii]
+        return 0 if i.nil?
+        a[i], a[k] = a[k], a[i]
         akk = a[k][k]
         det *= -1
       end