diff --git a/boefjes/katalogus/storage/memory.py b/boefjes/katalogus/storage/memory.py
index e5cae86..910ef21 100644
--- a/boefjes/katalogus/storage/memory.py
+++ b/boefjes/katalogus/storage/memory.py
@@ -74,10 +74,10 @@ def get_all(self, organisation_id: str, plugin_id: str) -> Dict[str, str]:
         return {k.split(".", maxsplit=1)[1]: v for k, v in self._data[organisation_id].items() if plugin_id in k}
 
     def create(self, key: str, value: str, organisation_id: str, plugin_id: str) -> None:
-        self._data[organisation_id][f"{plugin_id}.{key}"] = value
+        self._data[organisation_id][f"{plugin_id}.{key}"] = str(value)
 
     def update_by_key(self, key: str, value: str, organisation_id: str, plugin_id: str) -> None:
-        self._data[organisation_id][f"{plugin_id}.{key}"] = value
+        self._data[organisation_id][f"{plugin_id}.{key}"] = str(value)
 
     def delete_by_key(self, key: str, organisation_id: str, plugin_id: str) -> None:
         del self._data[organisation_id][f"{plugin_id}.{key}"]
diff --git a/boefjes/katalogus/tests/boefjes_test_dir/kat_test/kat_test_2/schema.json b/boefjes/katalogus/tests/boefjes_test_dir/kat_test/kat_test_2/schema.json
index 236004f..7f1e42c 100644
--- a/boefjes/katalogus/tests/boefjes_test_dir/kat_test/kat_test_2/schema.json
+++ b/boefjes/katalogus/tests/boefjes_test_dir/kat_test/kat_test_2/schema.json
@@ -5,10 +5,15 @@
     "api_key": {
       "title": "Api Key",
       "maxLength": 128,
+      "type": "integer"
+    },
+    "optional_key": {
+      "title": "Optional Key",
+      "maxLength": 128,
       "type": "string"
     }
   },
   "required": [
     "api_key"
   ]
-}
\ No newline at end of file
+}
diff --git a/boefjes/katalogus/tests/test_plugin_service.py b/boefjes/katalogus/tests/test_plugin_service.py
index a008186..9ebbbcb 100644
--- a/boefjes/katalogus/tests/test_plugin_service.py
+++ b/boefjes/katalogus/tests/test_plugin_service.py
@@ -206,3 +206,23 @@ def test_removing_mandatory_setting_disables_plugin(self):
 
         plugin = self.service.by_plugin_id(plugin_id, self.organisation)
         self.assertFalse(plugin.enabled)
+
+    def test_adding_integer_settings_with_faulty_value_given_constraints(self):
+        plugin_id = "kat_test_2"
+
+        self.service.settings_storage.update_by_key("api_key", "24", self.organisation, plugin_id)
+
+        with self.assertRaises(SettingsNotConformingToSchema) as ctx:
+            self.service.update_by_id("test-repo-2", plugin_id, self.organisation, True)
+
+        self.assertIn("'24' is not of type 'integer'", ctx.exception.message)
+
+        self.service.settings_storage.update_by_key("api_key", 24, self.organisation, plugin_id)  # Will become a string
+
+        with self.assertRaises(SettingsNotConformingToSchema) as ctx:
+            self.service.update_by_id("test-repo-2", plugin_id, self.organisation, True)
+
+        self.assertIn("'24' is not of type 'integer'", ctx.exception.message)
+
+        plugin = self.service.by_plugin_id(plugin_id, self.organisation)
+        self.assertFalse(plugin.enabled)
diff --git a/boefjes/plugins/kat_nmap/schema.json b/boefjes/plugins/kat_nmap/schema.json
index 2900904..5d3854f 100644
--- a/boefjes/plugins/kat_nmap/schema.json
+++ b/boefjes/plugins/kat_nmap/schema.json
@@ -4,7 +4,7 @@
     "properties": {
         "TOP_PORTS": {
             "title": "TOP_PORTS",
-            "type": "integer",
+            "type": "string",
             "description": "Scan TOP_PORTS most common ports. Defaults to 250."
         },
         "PROTOCOL": {
@@ -14,7 +14,5 @@
             "description": "Scan 'udp' or 'tcp'. Defaults to 'tcp'."
         }
     },
-    "required": [
-
-    ]
-}
\ No newline at end of file
+    "required": []
+}