diff --git a/sha1.py b/sha1.py
index 5b01ddd..1b5d2ff 100755
--- a/sha1.py
+++ b/sha1.py
@@ -143,7 +143,7 @@ def _produce_digest(self):
         return _process_chunk(message[64:], *h)
 
 
-def sha1(data):
+def sha1(data=b''):
     """SHA-1 Hashing Function
 
     A custom SHA-1 hashing function implemented entirely in Python.