diff --git a/src/shamira.py b/src/shamira.py
--- a/src/shamira.py
+++ b/src/shamira.py
@@ -9,7 +9,8 @@ import gf256
 
 
 def _shareByte(secretB,k,n):
-	assert k<=n<255
+	if not k<=n<255:
+		raise ValueError("failing k<=n<255, k={0}, n={1}".format(k,n))
 	coefs=[int(secretB)]+[int(b) for b in os.urandom(k-1)]
 	points=[gf256.evaluate(coefs,i) for i in range(1,n+1)]
 	return points