diff --git a/gns3server/controller/appliance.py b/gns3server/controller/appliance.py
index 82c4064c..2d9986ef 100644
--- a/gns3server/controller/appliance.py
+++ b/gns3server/controller/appliance.py
@@ -73,12 +73,16 @@ class Appliance:
         """
         Appliance data (a hash)
         """
+        try:
+            category = ID_TO_CATEGORY[self._data["category"]]
+        except KeyError:
+            category = self._data["category"]
         return {
             "appliance_id": self._id,
             "node_type": self._data["node_type"],
             "name": self._data["name"],
             "default_name_format": self._data.get("default_name_format", "{name}-{0}"),
-            "category": ID_TO_CATEGORY[self._data["category"]],
+            "category": category,
             "symbol": self._data.get("symbol", ":/symbols/computer.svg"),
             "compute_id": self.compute_id,
             "builtin": self._builtin
diff --git a/tests/controller/test_appliance.py b/tests/controller/test_appliance.py
index ce35e29e..3ed325a0 100644
--- a/tests/controller/test_appliance.py
+++ b/tests/controller/test_appliance.py
@@ -39,6 +39,27 @@ def test_appliance_json():
     }
 
 
+def test_appliance_json_with_not_known_category():
+    a = Appliance(None, {
+        "node_type": "qemu",
+        "name": "Test",
+        "default_name_format": "{name}-{0}",
+        "category": 'Not known',
+        "symbol": "qemu.svg",
+        "server": "local"
+    })
+    assert a.__json__() == {
+        "appliance_id": a.id,
+        "node_type": "qemu",
+        "builtin": False,
+        "name": "Test",
+        "default_name_format": "{name}-{0}",
+        "category": "Not known",
+        "symbol": "qemu.svg",
+        "compute_id": "local"
+    }
+
+
 def test_appliance_fix_linked_base():
     """
     Version of the gui before 2.1 use linked_base and the server