diff --git a/pygridsynth/gridsynth.py b/pygridsynth/gridsynth.py
index 8ea87d5..53e3841 100644
--- a/pygridsynth/gridsynth.py
+++ b/pygridsynth/gridsynth.py
@@ -13,6 +13,7 @@
 
 class EpsilonRegion(ConvexSet):
     def __init__(self, theta, epsilon):
+        epsilon = mpmath.mpf(epsilon)
         self._theta = theta
         self._epsilon = epsilon
         self._d = 1 - epsilon ** 2 / 2