diff --git a/pymc_bart/bart.py b/pymc_bart/bart.py
index 16a856c..94b91c3 100644
--- a/pymc_bart/bart.py
+++ b/pymc_bart/bart.py
@@ -25,6 +25,7 @@
 from pymc.distributions.distribution import Distribution, _support_point
 from pymc.logprob.abstract import _logprob
 from pytensor.tensor.random.op import RandomVariable
+from pytensor.tensor.sharedvar import TensorSharedVariable
 
 from .split_rules import SplitRule
 from .tree import Tree
@@ -53,11 +54,16 @@ def rng_fn(  # pylint: disable=W0237
         if not size:
             size = None
 
+        if isinstance(cls.Y, TensorSharedVariable):
+            Y = cls.Y.eval()
+        else:
+            Y = cls.Y
+
         if not cls.all_trees:
             if size is not None:
-                return np.full((size[0], cls.Y.shape[0]), cls.Y.mean())
+                return np.full((size[0], Y.shape[0]), Y.mean())
             else:
-                return np.full(cls.Y.shape[0], cls.Y.mean())
+                return np.full(Y.shape[0], Y.mean())
         else:
             if size is not None:
                 shape = size[0]