diff --git a/apps/transport/lib/validators/netex_validator.ex b/apps/transport/lib/validators/netex_validator.ex
index 7fceddbd98..9e9d05daf1 100644
--- a/apps/transport/lib/validators/netex_validator.ex
+++ b/apps/transport/lib/validators/netex_validator.ex
@@ -249,10 +249,15 @@ defmodule Transport.Validators.NeTEx do
 
   iex> index_messages([%{"code"=>"a", "id"=> 1}, %{"code"=>"a", "id"=> 2}, %{"code"=>"b", "id"=> 3}])
   %{"a"=>[%{"code"=>"a", "id"=> 1}, %{"code"=>"a", "id"=> 2}], "b"=>[%{"code"=>"b", "id"=> 3}]}
+
+  Sometimes the message has no code
+  iex> index_messages([%{"code"=>"a", "id"=> 1}, %{"code"=>"b", "id"=> 2}, %{"id"=> 3}])
+  %{"a"=>[%{"code"=>"a", "id"=> 1}], "b"=>[%{"code"=>"b", "id"=> 2}], "unknown-code"=>[%{"id"=> 3}]}
   """
-  def index_messages(messages) do
-    messages |> Enum.group_by(fn %{"code" => code} -> code end)
-  end
+  def index_messages(messages), do: Enum.group_by(messages, &get_code/1)
+
+  defp get_code(%{"code" => code}), do: code
+  defp get_code(%{}), do: "unknown-code"
 
   # This will change with an actual versioning of the validator
   def validator_version, do: "saas-production"
@@ -298,7 +303,8 @@ defmodule Transport.Validators.NeTEx do
       "longitude-mandatory" => dgettext("netex-validator", "Longitude mandatory"),
       "uic-operating-period" => dgettext("netex-validator", "UIC operating period"),
       "valid-day-bits" => dgettext("netex-validator", "Valid day bits"),
-      "version-any" => dgettext("netex-validator", "Version any")
+      "version-any" => dgettext("netex-validator", "Version any"),
+      "unknown-code" => dgettext("netex-validator", "Unspecified error")
     }
 
   @doc """
@@ -347,17 +353,20 @@ defmodule Transport.Validators.NeTEx do
 
   defp demote_non_xsd_errors(errors), do: Enum.map(errors, &demote_non_xsd_error(&1))
 
-  defp demote_non_xsd_error(%{"criticity" => criticity, "code" => code} = error) do
-    criticity =
-      if String.starts_with?(code, "xsd-") do
-        criticity
-      else
-        case criticity do
-          "error" -> "warning"
-          _ -> criticity
-        end
-      end
+  defp demote_non_xsd_error(error) do
+    code = Map.get(error, "code", "")
 
-    Map.update!(error, "criticity", fn _ -> criticity end)
+    if String.starts_with?(code, "xsd-") do
+      error
+    else
+      Map.update!(error, "criticity", &demote_error/1)
+    end
+  end
+
+  defp demote_error(criticity) do
+    case criticity do
+      "error" -> "warning"
+      _ -> criticity
+    end
   end
 end
diff --git a/apps/transport/priv/gettext/en/LC_MESSAGES/netex-validator.po b/apps/transport/priv/gettext/en/LC_MESSAGES/netex-validator.po
index 8fefa80452..9d2dc078e6 100644
--- a/apps/transport/priv/gettext/en/LC_MESSAGES/netex-validator.po
+++ b/apps/transport/priv/gettext/en/LC_MESSAGES/netex-validator.po
@@ -66,3 +66,7 @@ msgstr ""
 #, elixir-autogen, elixir-format
 msgid "warnings"
 msgstr ""
+
+#, elixir-autogen, elixir-format
+msgid "Unspecified error"
+msgstr ""
diff --git a/apps/transport/priv/gettext/fr/LC_MESSAGES/netex-validator.po b/apps/transport/priv/gettext/fr/LC_MESSAGES/netex-validator.po
index 1886f4e5d8..7b30b0cebd 100644
--- a/apps/transport/priv/gettext/fr/LC_MESSAGES/netex-validator.po
+++ b/apps/transport/priv/gettext/fr/LC_MESSAGES/netex-validator.po
@@ -66,3 +66,7 @@ msgstr ""
 #, elixir-autogen, elixir-format
 msgid "warnings"
 msgstr "avertissements"
+
+#, elixir-autogen, elixir-format
+msgid "Unspecified error"
+msgstr ""
diff --git a/apps/transport/priv/gettext/netex-validator.pot b/apps/transport/priv/gettext/netex-validator.pot
index 2566320ef1..82d778082e 100644
--- a/apps/transport/priv/gettext/netex-validator.pot
+++ b/apps/transport/priv/gettext/netex-validator.pot
@@ -66,3 +66,7 @@ msgstr ""
 #, elixir-autogen, elixir-format
 msgid "warnings"
 msgstr ""
+
+#, elixir-autogen, elixir-format
+msgid "Unspecified error"
+msgstr ""
diff --git a/apps/transport/test/transport/validators/netex_validator_test.exs b/apps/transport/test/transport/validators/netex_validator_test.exs
index 20312562b5..70714a1755 100644
--- a/apps/transport/test/transport/validators/netex_validator_test.exs
+++ b/apps/transport/test/transport/validators/netex_validator_test.exs
@@ -35,6 +35,10 @@ defmodule Transport.Validators.NeTExTest do
       "code" => "frame-arret-resources",
       "message" => "Tag frame_id doesn't match ''",
       "criticity" => "warning"
+    },
+    %{
+      "message" => "Reference MOBIITI:Quay:104325 doesn't match any existing Resource",
+      "criticity" => "error"
     }
   ]
 
@@ -104,6 +108,12 @@ defmodule Transport.Validators.NeTExTest do
                    "message" => "Tag frame_id doesn't match ''",
                    "criticity" => "warning"
                  }
+               ],
+               "unknown-code" => [
+                 %{
+                   "message" => "Reference MOBIITI:Quay:104325 doesn't match any existing Resource",
+                   "criticity" => "warning"
+                 }
                ]
              }
     end
@@ -163,6 +173,12 @@ defmodule Transport.Validators.NeTExTest do
             "message" => "Tag frame_id doesn't match ''",
             "criticity" => "warning"
           }
+        ],
+        "unknown-code" => [
+          %{
+            "message" => "Reference MOBIITI:Quay:104325 doesn't match any existing Resource",
+            "criticity" => "warning"
+          }
         ]
       }