diff --git a/abcpy/models.py b/abcpy/models.py
index a8931b57..9cd6179b 100644
--- a/abcpy/models.py
+++ b/abcpy/models.py
@@ -118,10 +118,9 @@ def __init__(self, prior, mu = None, sigma = None, seed=None):
             Initial seed. The default value is generated randomly.
         """
 
-        # test and set prior
+        # test prior
         if np.shape(prior.sample(1)) == (1,2):
             self.prior = prior
-            self.sample_from_prior()
         else:
             raise ValueError("Prior generates values outside the model "
                              "parameter domain. ")
@@ -134,6 +133,9 @@ def __init__(self, prior, mu = None, sigma = None, seed=None):
         if mu != None and sigma != None:
             if self.set_parameters(np.array([mu, sigma])) == False:
                 raise ValueError("The parameter values are out of the model parameter domain.")
+        else:
+            self.sample_from_prior()
+
 
         # set random number generator
         self.rng = np.random.RandomState(seed)