diff --git a/requirements.py3.txt b/requirements.py3.txt
index c457606..d150550 100644
--- a/requirements.py3.txt
+++ b/requirements.py3.txt
@@ -32,6 +32,9 @@ stripe
 # PayPal REST API SDK for payments.
 paypalrestsdk
 
+# Adyen payment processing SDK.
+Adyen
+
 # DKIM Signed Email from Python, lot's of extras in here like async.
 # https://git.launchpad.net/dkimpy/tree/setup.py#n84
 dkimpy