diff --git a/GPy/plotting/gpy_plot/plot_util.py b/GPy/plotting/gpy_plot/plot_util.py
index 4e71a3bc..ec312feb 100644
--- a/GPy/plotting/gpy_plot/plot_util.py
+++ b/GPy/plotting/gpy_plot/plot_util.py
@@ -379,5 +379,5 @@ def x_frame2D(X,plot_limits=None,resolution=None):
 
     resolution = resolution or 50
     xx, yy = np.mgrid[xmin[0]:xmax[0]:1j*resolution,xmin[1]:xmax[1]:1j*resolution]
-    Xnew = np.vstack((xx.flatten(),yy.flatten())).T
+    Xnew = np.c_[xx.flat, yy.flat]
     return Xnew, xx, yy, xmin, xmax
\ No newline at end of file