diff --git a/dkim/__init__.py b/dkim/__init__.py
index 3ff305c..81e502c 100644
--- a/dkim/__init__.py
+++ b/dkim/__init__.py
@@ -15,6 +15,8 @@
 # 3. This notice may not be removed or altered from any source distribution.
 #
 # Copyright (c) 2008 Greg Hewgill http://hewgill.com
+#
+# This has been modified from the original software.
 # Copyright (c) 2011 William Grant <me@williamgrant.id.au>
 
 import base64
diff --git a/dkim/asn1.py b/dkim/asn1.py
index 7aa4c00..43387b9 100644
--- a/dkim/asn1.py
+++ b/dkim/asn1.py
@@ -15,6 +15,8 @@
 # 3. This notice may not be removed or altered from any source distribution.
 #
 # Copyright (c) 2008 Greg Hewgill http://hewgill.com
+#
+# This has been modified from the original software.
 # Copyright (c) 2011 William Grant <me@williamgrant.id.au>
 
 __all__ = [
diff --git a/dkim/crypto.py b/dkim/crypto.py
index 29d734a..b7011d3 100644
--- a/dkim/crypto.py
+++ b/dkim/crypto.py
@@ -15,6 +15,8 @@
 # 3. This notice may not be removed or altered from any source distribution.
 #
 # Copyright (c) 2008 Greg Hewgill http://hewgill.com
+#
+# This has been modified from the original software.
 # Copyright (c) 2011 William Grant <me@williamgrant.id.au>
 
 __all__ = [
diff --git a/setup.py b/setup.py
index dc2ef47..5b8ee60 100644
--- a/setup.py
+++ b/setup.py
@@ -37,7 +37,7 @@ Identified Mail) email signing and verification.""",
     author_email = "greg@hewgill.com",
     url = "http://hewgill.com/pydkim/",
     license = "BSD-like",
-    py_modules = ["dkim"],
+    packages = ["dkim"],
     scripts = ["dkimsign.py", "dkimverify.py", "dkimsend.sh"],
     data_files = [(os.path.join('share', 'man', 'man1'),
         ['man/dkimsign.1']), (os.path.join('share', 'man', 'man1'),