diff --git a/CHANGES.txt b/CHANGES.txt
index fb876491d..70046378e 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -12,6 +12,8 @@ Revision 4.4.7, released 2018-12-29
   sending SNMPv3 TRAP with non-default `contextName` would fail.
 - Fixed possible duplicate key occurrence in the `OrderedDict` following
   a race condition
+- Fixed undefined name references in `inet_pton`/`inet_ntop` substitute
+  routines for IPv6 in `TRANSPORT-ADDRESS-MIB.py`
 
 Revision 4.4.6, released 2018-09-13
 -----------------------------------
diff --git a/pysnmp/smi/mibs/TRANSPORT-ADDRESS-MIB.py b/pysnmp/smi/mibs/TRANSPORT-ADDRESS-MIB.py
index 38d12699a..213bb89c0 100644
--- a/pysnmp/smi/mibs/TRANSPORT-ADDRESS-MIB.py
+++ b/pysnmp/smi/mibs/TRANSPORT-ADDRESS-MIB.py
@@ -36,7 +36,7 @@
 
         def inet_pton(address_family, ip_string):
             if address_family == socket.AF_INET:
-                return inet_aton(ip_string)
+                return socket.inet_aton(ip_string)
             elif address_family != socket.AF_INET6:
                 raise socket.error(
                     'Unknown address family %s' % (address_family,)
@@ -46,7 +46,7 @@ def inet_pton(address_family, ip_string):
             spaces = groups.count('')
 
             if '.' in groups[-1]:
-                groups[-1:] = ["%x" % x for x in struct.unpack("!HH", inet_aton(groups[-1]))]
+                groups[-1:] = ["%x" % x for x in struct.unpack("!HH", socket.inet_aton(groups[-1]))]
 
             if spaces == 1:
                 idx = groups.index('')
@@ -84,7 +84,7 @@ def inet_pton(address_family, ip_string):
 
         def inet_ntop(address_family, packed_ip):
             if address_family == socket.AF_INET:
-                return inet_ntop(packed_ip)
+                return socket.inet_ntop(packed_ip)
             elif address_family != socket.AF_INET6:
                 raise socket.error(
                     'Unknown address family %s' % (address_family,)