diff --git a/src/_secureaccesstokenauthorizer/resource.py b/src/_secureaccesstokenauthorizer/resource.py
index d8b3626e862d35dbb034345344af368ebbb947cf..f1e59d8e9f4752ccb7b31c8653570dc50d18d347 100644
--- a/src/_secureaccesstokenauthorizer/resource.py
+++ b/src/_secureaccesstokenauthorizer/resource.py
@@ -79,11 +79,11 @@ def from_configuration(node_config, store=None):
 
 class _PaymentReferenceNumberCollection(Resource):
     """
-    This class implements redemption of payment reference numbers (PRNs).
-    Users **PUT** such numbers to this resource which delegates redemption
+    This class implements redemption of payment reference numbers.  Users
+    **PUT** such numbers to this resource which delegates redemption
     responsibilities to the redemption controller.  Child resources of this
     resource can also be retrieved to monitor the status of previously
-    submitted PRNs.
+    submitted vouchers.
     """
     def __init__(self, store, controller):
         self._store = store
@@ -93,7 +93,7 @@ class _PaymentReferenceNumberCollection(Resource):
 
     def render_PUT(self, request):
         """
-        Record a PRN and begin attempting to redeem it.
+        Record a voucher and begin attempting to redeem it.
         """
         try:
             payload = loads(request.content.read())
@@ -137,9 +137,9 @@ def is_syntactic_prn(prn):
 
     :return bool: ``True`` if and only if ``prn`` is a unicode string
         containing a syntactically valid payment reference number.  This says
-        **nothing** about the validity of the represented PRN itself.  A
+        **nothing** about the validity of the represented voucher itself.  A
         ``True`` result only means the unicode string can be **interpreted**
-        as a PRN.
+        as a voucher.
     """
     if not isinstance(prn, unicode):
         return False
diff --git a/src/_secureaccesstokenauthorizer/tests/test_client_resource.py b/src/_secureaccesstokenauthorizer/tests/test_client_resource.py
index 3bd4812c4fc639e510eb0227b809f002f9647645..176d6ce0a09625d06dcfa46ce1db37a9d1d92041 100644
--- a/src/_secureaccesstokenauthorizer/tests/test_client_resource.py
+++ b/src/_secureaccesstokenauthorizer/tests/test_client_resource.py
@@ -147,9 +147,9 @@ def not_payment_reference_numbers():
             ),
         ),
         payment_reference_numbers().map(
-            # Turn a valid PRN into a PRN that is invalid only by containing a
-            # character from the base64 alphabet in place of one from the
-            # urlsafe-base64 alphabet.
+            # Turn a valid voucher into a voucher that is invalid only by
+            # containing a character from the base64 alphabet in place of one
+            # from the urlsafe-base64 alphabet.
             lambda prn: u"/" + prn[1:],
         ),
     )
@@ -210,7 +210,7 @@ class PaymentReferenceNumberTests(TestCase):
     """
     Tests relating to ``/payment-reference-number`` as implemented by the
     ``_secureaccesstokenauthorizer.resource`` module and its handling of
-    payment reference numbers (PRNs).
+    payment reference numbers.
     """
     def setUp(self):
         super(PaymentReferenceNumberTests, self).setUp()
@@ -235,9 +235,9 @@ class PaymentReferenceNumberTests(TestCase):
     @given(tahoe_configs_with_client_config, payment_reference_numbers())
     def test_put_prn(self, get_config, prn):
         """
-        When a PRN is sent in a ``PUT`` to ``PaymentReferenceNumberCollection`` it
-        is passed in to the PRN redemption model object for handling and an
-        ``OK`` response is returned.
+        When a voucher is ``PUT`` to ``PaymentReferenceNumberCollection`` it is
+        passed in to the redemption model object for handling and an ``OK``
+        response is returned.
         """
         tempdir = self.useFixture(TempDir())
         config = get_config(tempdir.join(b"tahoe"), b"tub.port")
@@ -297,8 +297,9 @@ class PaymentReferenceNumberTests(TestCase):
     @given(tahoe_configs_with_client_config, not_payment_reference_numbers())
     def test_get_invalid_prn(self, get_config, not_prn):
         """
-        When a syntactically invalid PRN is requested with a ``GET`` to a child of
-        ``PaymentReferenceNumberCollection`` the response is **BAD REQUEST**.
+        When a syntactically invalid voucher is requested with a ``GET`` to a
+        child of ``PaymentReferenceNumberCollection`` the response is **BAD
+        REQUEST**.
         """
         tempdir = self.useFixture(TempDir())
         config = get_config(tempdir.join(b"tahoe"), b"tub.port")
@@ -325,9 +326,9 @@ class PaymentReferenceNumberTests(TestCase):
     @given(tahoe_configs_with_client_config, payment_reference_numbers())
     def test_get_unknown_prn(self, get_config, prn):
         """
-        When a PRN is requested with a ``GET`` to a child of
+        When a voucher is requested with a ``GET`` to a child of
         ``PaymentReferenceNumberCollection`` the response is **NOT FOUND** if
-        the PRN hasn't previously been submitted with a ``PUT``.
+        the voucher hasn't previously been submitted with a ``PUT``.
         """
         tempdir = self.useFixture(TempDir())
         config = get_config(tempdir.join(b"tahoe"), b"tub.port")
@@ -348,9 +349,9 @@ class PaymentReferenceNumberTests(TestCase):
     @given(tahoe_configs_with_client_config, payment_reference_numbers())
     def test_get_known_prn(self, get_config, prn):
         """
-        When a PRN is first ``PUT`` and then later a ``GET`` is issued for the
-        same PRN then the response code is **OK** and details about the PRN
-        are included in a json-encoded response body.
+        When a voucher is first ``PUT`` and then later a ``GET`` is issued for the
+        same voucher then the response code is **OK** and details about the
+        voucher are included in a json-encoded response body.
         """
         tempdir = self.useFixture(TempDir())
         config = get_config(tempdir.join(b"tahoe"), b"tub.port")
@@ -416,7 +417,7 @@ class PaymentReferenceNumberTests(TestCase):
         root = root_from_config(config)
         agent = RequestTraversalAgent(root)
 
-        note("{} PRNs".format(len(prns)))
+        note("{} vouchers".format(len(prns)))
 
         for prn in prns:
             producer = FileBodyProducer(