diff --git a/paymentwall/pingback.py b/paymentwall/pingback.py
index f5bbf84..75e678e 100644
--- a/paymentwall/pingback.py
+++ b/paymentwall/pingback.py
@@ -189,4 +189,4 @@ def calculate_signature(self, params, secret, version):
 
 		base_string += secret
 
-		return self.hash(base_string.encode('utf-8'), 'sha256') if int(version) == self.SIGNATURE_VERSION_3 else self.hash(base_string.encode('utf-8'), 'md5')
+		return self.hash(base_string, 'sha256') if int(version) == self.SIGNATURE_VERSION_3 else self.hash(base_string, 'md5')