diff --git a/GPy/core/gp.py b/GPy/core/gp.py
index ca2583e0..e67125e7 100644
--- a/GPy/core/gp.py
+++ b/GPy/core/gp.py
@@ -33,13 +33,13 @@ class GP(Model):
 
         assert X.ndim == 2
         if isinstance(X, (ObsAr, VariationalPosterior)):
-            self.X = X
-        else: self.X = ObsAr(X)
+            self.X = X.copy()
+        else: self.X = ObsAr(X.copy())
 
         self.num_data, self.input_dim = self.X.shape
 
         assert Y.ndim == 2
-        self.Y = ObsAr(Y)
+        self.Y = ObsAr(Y.copy())
         assert Y.shape[0] == self.num_data
         _, self.output_dim = self.Y.shape