diff --git a/examples/bffh.dhall b/examples/bffh.dhall
index 4a57c51..249f473 100644
--- a/examples/bffh.dhall
+++ b/examples/bffh.dhall
@@ -33,7 +33,8 @@
   ]
 , machines = 
   { Testmachine = 
-    { description = Some "A test machine"
+    { description = "A test machine"
+    , wiki = "test"
     , disclose = "lab.test.read"
     , manage = "lab.test.admin"
     , name = "MachineA"
@@ -41,7 +42,7 @@
     , write = "lab.test.write" 
     },
     Another = 
-    { description = Some "Another test machine"
+    { wiki = "test_another"
     , disclose = "lab.test.read"
     , manage = "lab.test.admin"
     , name = "Another"
@@ -49,7 +50,7 @@
     , write = "lab.test.write" 
     },
     Yetmore = 
-    { description = Some "Yet more test machines"
+    { description = "Yet more test machines"
     , disclose = "lab.test.read"
     , manage = "lab.test.admin"
     , name = "Yetmore"
diff --git a/src/machine.rs b/src/machine.rs
index 255c669..9bd53c7 100644
--- a/src/machine.rs
+++ b/src/machine.rs
@@ -352,6 +352,7 @@ impl Inner {
 }
 
 #[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(deny_unknown_fields)]
 /// A description of a machine
 ///
 /// This is the struct that a machine is serialized to/from.
@@ -359,11 +360,12 @@ impl Inner {
 pub struct MachineDescription {
     /// The name of the machine. Doesn't need to be unique but is what humans will be presented.
     pub name: String,
+
     /// An optional description of the Machine.
+    #[serde(default, skip_serializing_if = "Option::is_none", deserialize_with = "deser_option")]
     pub description: Option<String>,
 
-    #[serde(default)]
-    #[serde(flatten)]
+    #[serde(default, skip_serializing_if = "Option::is_none", deserialize_with = "deser_option")]
     pub wiki: Option<String>,
 
     /// The permission required
@@ -371,6 +373,12 @@ pub struct MachineDescription {
     pub privs: access::PrivilegesBuf,
 }
 
+fn deser_option<'de, D, T>(d: D) -> std::result::Result<Option<T>, D::Error>
+    where D: serde::Deserializer<'de>, T: serde::Deserialize<'de>,
+{
+    Ok(T::deserialize(d).ok())
+}
+
 impl MachineDescription {
     pub fn load_file<P: AsRef<Path>>(path: P) -> Result<HashMap<MachineIdentifier, MachineDescription>> {
         let content = fs::read(path)?;