diff --git a/GPy/core/gp.py b/GPy/core/gp.py
index 05e3e671..70b7d695 100644
--- a/GPy/core/gp.py
+++ b/GPy/core/gp.py
@@ -42,7 +42,10 @@ class GP(Model):
         assert Y.shape[0] == self.num_data
         _, self.output_dim = self.Y.shape
 
-        self.Y_metadata = Y_metadata or {}
+        if Y_metadata is None:
+            Y_metadata = {}
+        else:
+            self.Y_metadata = Y_metadata
 
         assert isinstance(kernel, kern.Kern)
         #assert self.input_dim == kernel.input_dim