diff --git a/matlab/k_order_pert.m b/matlab/k_order_pert.m
index 99de060c5..2fada0a73 100644
--- a/matlab/k_order_pert.m
+++ b/matlab/k_order_pert.m
@@ -143,7 +143,7 @@ for i=1:n
             y(:,(i-1)*n*n+(j-1)*n+k) = xx;
             y(:,(i-1)*n*n+(k-1)*n+j) = xx;
             y(:,(j-1)*n*n+(k-1)*n+i) = xx;
-            y(:,(i-1)*n*n+(k-1)*n+j) = xx;
+            y(:,(j-1)*n*n+(i-1)*n+k) = xx;
             y(:,(k-1)*n*n+(i-1)*n+j) = xx;
             y(:,(k-1)*n*n+(j-1)*n+i) = xx;
             m = m + 1;