diff --git a/peyote/prior.py b/peyote/prior.py
index ff69acd292c6a361ed410a196d525223d903b8fb..1ef3a098306fa8485cac2ec43aa3380b5cd915a7 100644
--- a/peyote/prior.py
+++ b/peyote/prior.py
@@ -145,15 +145,21 @@ class PowerLaw(Prior):
         This maps to the inverse CDF. This has been analytically solved for this case.
         """
         if self.alpha == -1:
-            return self.low * np.exp(val * np.log(self.low / self.high))
+            return self.low * np.exp(val * np.log(self.high / self.low))
         else:
             return (self.low ** (1 + self.alpha) + val *
                     (self.high ** (1 + self.alpha) - self.low ** (1 + self.alpha))) ** (1. / (1 + self.alpha))
 
     def prob(self, val):
         """Return the prior probability of val"""
-        return val ** self.alpha * (1 + self.alpha) / (self.high ** (1 + self.alpha) -
-                                                       self.low ** (1 + self.alpha))
+        if (val > self.low) and (val < self.high):
+            if self.alpha == -1:
+                return 1 / val / np.log(self.high / self.low)
+            else:
+                return val ** self.alpha * (1 + self.alpha) / (self.high ** (1 + self.alpha)
+                                                               - self.low ** (1 + self.alpha))
+        else:
+            return 0
 
 
 class Cosine(Prior):