diff --git a/tests/scripts/thread-cert/mesh_cop.py b/tests/scripts/thread-cert/mesh_cop.py
index 36544f351..3f2d1dfa9 100644
--- a/tests/scripts/thread-cert/mesh_cop.py
+++ b/tests/scripts/thread-cert/mesh_cop.py
@@ -30,9 +30,11 @@
 from binascii import hexlify
 from enum import IntEnum
 import io
+import logging
 import struct
 
 from network_data import SubTlvsFactory
+from tlvs_parsing import UnknownTlvFactory
 import common
 
 
@@ -931,9 +933,10 @@ class MeshCopCommandFactory:
         try:
             return self._tlvs_factories[_type]
         except KeyError:
-            raise KeyError(
-                "Could not find TLV factory. Unsupported TLV type: {}".format(
+            logging.error(
+                'Could not find TLV factory. Unsupported TLV type: {}'.format(
                     _type))
+            return UnknownTlvFactory(_type)
 
     def _parse_tlv(self, data):
         _type = TlvType(ord(data.read(1)))
diff --git a/tests/scripts/thread-cert/mle.py b/tests/scripts/thread-cert/mle.py
index e075be141..c47f19056 100644
--- a/tests/scripts/thread-cert/mle.py
+++ b/tests/scripts/thread-cert/mle.py
@@ -28,6 +28,7 @@
 #
 
 import io
+import logging
 import struct
 
 from binascii import hexlify
@@ -35,6 +36,7 @@ from binascii import hexlify
 import common
 
 from enum import IntEnum
+from tlvs_parsing import UnknownTlvFactory
 
 
 class CommandType(IntEnum):
@@ -452,15 +454,13 @@ class LeaderData(object):
                 self.leader_router_id == other.leader_router_id)
 
     def __repr__(self):
-        return (
-            "LeaderData(partition_id={}, weighting={}, data_version={}, stable_data_version={},",
-            "leader_router_id={})").format(
-                self.partition_id,
-                self.weighting,
-                self.data_version,
-                self.stable_data_version,
-                self.leader_router_id,
-            )
+        return 'LeaderData(partition_id={}, weighting={}, data_version={}, stable_data_version={},leader_router_id={}'.format(
+            self.partition_id,
+            self.weighting,
+            self.data_version,
+            self.stable_data_version,
+            self.leader_router_id,
+        )
 
 
 class LeaderDataFactory:
@@ -1138,9 +1138,10 @@ class MleCommandFactory:
         try:
             return self._tlvs_factories[_type]
         except KeyError:
-            raise KeyError(
-                "Could not find TLV factory. Unsupported TLV type: {}".format(
+            logging.error(
+                'Could not find TLV factory. Unsupported TLV type: {}'.format(
                     _type))
+            return UnknownTlvFactory(_type)
 
     def _parse_tlv(self, data, message_info):
         _type = TlvType(ord(data.read(1)))
diff --git a/tests/scripts/thread-cert/tlvs_parsing.py b/tests/scripts/thread-cert/tlvs_parsing.py
index 5c9920d53..5ca8f7c5c 100644
--- a/tests/scripts/thread-cert/tlvs_parsing.py
+++ b/tests/scripts/thread-cert/tlvs_parsing.py
@@ -27,6 +27,26 @@
 #  POSSIBILITY OF SUCH DAMAGE.
 
 import io
+import logging
+
+
+class UnknownTlv(object):
+
+    def __init__(self, type, data):
+        self.type = type
+        self.data = data
+
+    def __repr__(self):
+        return 'UnknownTlv(%d, %s)' % (self.type, self.data)
+
+
+class UnknownTlvFactory(object):
+
+    def __init__(self, type):
+        self._type = type
+
+    def parse(self, data, message_info):
+        return UnknownTlv(self._type, data)
 
 
 class SubTlvsFactory(object):
@@ -38,8 +58,10 @@ class SubTlvsFactory(object):
         try:
             return self._sub_tlvs_factories[_type]
         except KeyError:
-            raise RuntimeError(
-                "Could not find factory. Factory type = {}.".format(_type))
+            logging.error(
+                'Could not find TLV factory. Unsupported TLV type: {}'.format(
+                    _type))
+            return UnknownTlvFactory(_type)
 
     def parse(self, data, message_info):
         sub_tlvs = []