diff --git a/GPy/core/parameterization/variational.py b/GPy/core/parameterization/variational.py
index d204b166..44b48ccb 100644
--- a/GPy/core/parameterization/variational.py
+++ b/GPy/core/parameterization/variational.py
@@ -7,7 +7,7 @@ Created on 6 Nov 2013
 import numpy as np
 from parameterized import Parameterized
 from param import Param
-from transformations import Logexp
+from transformations import Logexp, Logistic
 
 class VariationalPrior(Parameterized):
     def __init__(self, name=None, **kw):
@@ -37,7 +37,7 @@ class SpikeAndSlabPrior(VariationalPrior):
     def __init__(self, pi, variance = 1.0, name='SpikeAndSlabPrior', **kw):
         super(VariationalPrior, self).__init__(name=name, **kw)
         assert variance==1.0, "Not Implemented!"
-        self.pi = Param('pi', pi)
+        self.pi = Param('pi', pi, Logistic(1e-10,1-1e-10))
         self.variance = Param('variance',variance)
         self.add_parameters(self.pi)
         
@@ -105,7 +105,7 @@ class SpikeAndSlabPosterior(VariationalPosterior):
         binary_prob : the probability of the distribution on the slab part.
         """
         super(SpikeAndSlabPosterior, self).__init__(means, variances, name)
-        self.gamma = Param("binary_prob",binary_prob,)
+        self.gamma = Param("binary_prob",binary_prob, Logistic(1e-10,1-1e-10))
         self.add_parameter(self.gamma)
 
     def plot(self, *args):