diff --git a/baselines/common/distributions.py b/baselines/common/distributions.py
index 8366eb5edc..491b9ff9be 100644
--- a/baselines/common/distributions.py
+++ b/baselines/common/distributions.py
@@ -53,6 +53,9 @@ def param_placeholder(self, prepend_shape, name=None):
     def sample_placeholder(self, prepend_shape, name=None):
         return tf.placeholder(dtype=self.sample_dtype(), shape=prepend_shape+self.sample_shape(), name=name)
 
+    def __eq__(self, other):
+        return (type(self) == type(other)) and (self.__dict__ == other.__dict__)
+
 class CategoricalPdType(PdType):
     def __init__(self, ncat):
         self.ncat = ncat