diff --git a/pycoax/coax/interface.py b/pycoax/coax/interface.py
index 5ae3b95..e001094 100644
--- a/pycoax/coax/interface.py
+++ b/pycoax/coax/interface.py
@@ -5,6 +5,8 @@ coax.interface
 
 from enum import Enum
 
+from .exceptions import ProtocolError
+
 class Interface:
     """3270 coax interface."""
 
@@ -106,7 +108,10 @@ def _unpack_inbound_frames(frames, commands):
         if isinstance(frame, BaseException):
             responses.append(frame)
         else:
-            response = command.unpack_inbound_frame(frame)
+            try:
+                response = command.unpack_inbound_frame(frame)
+            except ProtocolError as error:
+                response = error
 
             responses.append(response)
 
diff --git a/pycoax/tests/test_interface.py b/pycoax/tests/test_interface.py
index c9e5ea4..f9c9d8b 100644
--- a/pycoax/tests/test_interface.py
+++ b/pycoax/tests/test_interface.py
@@ -5,7 +5,7 @@ import context
 
 from coax.interface import Interface, FrameFormat
 from coax.protocol import ReadAddressCounterHi, ReadAddressCounterLo
-from coax.exceptions import ReceiveTimeout
+from coax.exceptions import InterfaceError, ReceiveTimeout, ProtocolError
 
 class InterfaceExecuteTestCase(unittest.TestCase):
     def setUp(self):
@@ -95,7 +95,23 @@ class InterfaceExecuteTestCase(unittest.TestCase):
 
         self.assertEqual(timeout, 0.1)
 
-    def test_single_command_exception(self):
+    def test_single_command_interface_error(self):
+        # Arrange
+        self.interface._transmit_receive.side_effect=InterfaceError()
+
+        # Act and assert
+        with self.assertRaises(InterfaceError):
+            self.interface.execute(ReadAddressCounterHi())
+
+    def test_multiple_command_interface_error(self):
+        # Arrange
+        self.interface._transmit_receive.side_effect=InterfaceError()
+
+        # Act and assert
+        with self.assertRaises(InterfaceError):
+            self.interface.execute([ReadAddressCounterHi(), ReadAddressCounterLo()])
+
+    def test_single_command_receive_timeout(self):
         # Arrange
         self.interface._transmit_receive.return_value=[ReceiveTimeout()]
 
@@ -103,5 +119,39 @@ class InterfaceExecuteTestCase(unittest.TestCase):
         with self.assertRaises(ReceiveTimeout):
             self.interface.execute(ReadAddressCounterHi())
 
+    def test_multiple_command_receive_timeout(self):
+        # Arrange
+        self.interface._transmit_receive.return_value=[[0b00000010_00], ReceiveTimeout()]
+
+        # Act
+        response = self.interface.execute([ReadAddressCounterHi(), ReadAddressCounterLo()])
+
+        # Assert
+        self.assertEqual(len(response), 2)
+
+        self.assertEqual(response[0], 0x02)
+        self.assertIsInstance(response[1], ReceiveTimeout)
+
+    def test_single_command_protocol_error(self):
+        # Arrange
+        self.interface._transmit_receive.return_value=[[0b00000010_01]]
+
+        # Act and assert
+        with self.assertRaises(ProtocolError):
+            self.interface.execute(ReadAddressCounterHi())
+
+    def test_multiple_command_protocol_error(self):
+        # Arrange
+        self.interface._transmit_receive.return_value=[[0b00000010_00], [0b00000010_01]]
+
+        # Act
+        response = self.interface.execute([ReadAddressCounterHi(), ReadAddressCounterLo()])
+
+        # Assert
+        self.assertEqual(len(response), 2)
+
+        self.assertEqual(response[0], 0x02)
+        self.assertIsInstance(response[1], ProtocolError)
+
 if __name__ == '__main__':
     unittest.main()