diff --git a/ocpp/exceptions.py b/ocpp/exceptions.py
index 6c570425f..e2e331cc4 100644
--- a/ocpp/exceptions.py
+++ b/ocpp/exceptions.py
@@ -35,14 +35,14 @@ def __str__(self):
 
 class NotImplementedError(OCPPError):
     code = "NotImplemented"
-    default_description = "Requested Action is not known by receiver"
+    default_description = (
+        "Request Action is recognized but not supported by the receiver"
+    )
 
 
 class NotSupportedError(OCPPError):
     code = "NotSupported"
-    default_description = (
-        "Request Action is recognized but not supported by " "the receiver"
-    )
+    default_description = "Requested Action is not known by receiver"
 
 
 class InternalError(OCPPError):
diff --git a/tests/v16/conftest.py b/tests/v16/conftest.py
index d747bf420..41c4eb290 100644
--- a/tests/v16/conftest.py
+++ b/tests/v16/conftest.py
@@ -16,6 +16,9 @@
 def heartbeat_call():
     return Call(unique_id=1, action=Action.Heartbeat, payload={}).to_json()
 
+@pytest.fixture
+def notsupported_call():
+    return Call(unique_id=1, action="InvalidAction", payload={}).to_json()
 
 @pytest.fixture
 def boot_notification_call():
diff --git a/tests/v16/test_v16_charge_point.py b/tests/v16/test_v16_charge_point.py
index 6e002ffe8..d08a6a408 100644
--- a/tests/v16/test_v16_charge_point.py
+++ b/tests/v16/test_v16_charge_point.py
@@ -125,13 +125,36 @@ async def test_route_message_with_no_route(base_central_system, heartbeat_call):
                 4,
                 1,
                 "NotImplemented",
-                "Requested Action is not known by receiver",
+                "Request Action is recognized but not supported by the receiver",
                 {"cause": "No handler for Heartbeat registered."},
             ],
             separators=(",", ":"),
         )
     )
 
+@pytest.mark.asyncio
+async def test_route_message_not_supported(base_central_system, notsupported_call):
+    """
+    Test that a CALLERROR is sent back, reporting that it is
+    not supported by OCPP version.
+
+    """
+    # Empty the route map
+    base_central_system.route_map = {}
+
+    await base_central_system.route_message(notsupported_call)
+    base_central_system._connection.send.assert_called_once_with(
+        json.dumps(
+            [
+                4,
+                1,
+                "NotSupported",
+                "Requested Action is not known by receiver",
+                {"cause": "InvalidAction not supported by OCPP1.6."},
+            ],
+            separators=(",", ":"),
+        )
+    )
 
 @pytest.mark.asyncio
 async def test_send_call_with_timeout(connection):
diff --git a/tests/v20/test_v20_charge_point.py b/tests/v20/test_v20_charge_point.py
index 56c49a9ec..bb0a04aa2 100644
--- a/tests/v20/test_v20_charge_point.py
+++ b/tests/v20/test_v20_charge_point.py
@@ -77,7 +77,7 @@ async def test_route_message_with_no_route(base_central_system, heartbeat_call):
                 4,
                 1,
                 "NotImplemented",
-                "Requested Action is not known by receiver",
+                "Request Action is recognized but not supported by the receiver",
                 {"cause": "No handler for Heartbeat registered."},
             ],
             separators=(",", ":"),
diff --git a/tests/v201/test_v201_charge_point.py b/tests/v201/test_v201_charge_point.py
index eacc22d7a..ddbd33808 100644
--- a/tests/v201/test_v201_charge_point.py
+++ b/tests/v201/test_v201_charge_point.py
@@ -77,7 +77,7 @@ async def test_route_message_with_no_route(base_central_system, heartbeat_call):
                 4,
                 1,
                 "NotImplemented",
-                "Requested Action is not known by receiver",
+                "Request Action is recognized but not supported by the receiver",
                 {"cause": "No handler for Heartbeat registered."},
             ],
             separators=(",", ":"),