diff --git a/target_redshift/s3.py b/target_redshift/s3.py
index eb64818..4d8e731 100644
--- a/target_redshift/s3.py
+++ b/target_redshift/s3.py
@@ -29,7 +29,7 @@ def credentials(self):
         return self._credentials
 
     def persist(self, readable, key_prefix=''):
-        key = self.key_prefix + key_prefix + str(uuid.uuid4()).replace('-', '')
+        key = self.key_prefix + (key_prefix or '') + str(uuid.uuid4()).replace('-', '')
 
         self.client.upload_fileobj(
             _EncodeBinaryReadable(readable),