diff --git a/src/api/core/two_factor.rs b/src/api/core/two_factor.rs
index 2669a8a..031711f 100644
--- a/src/api/core/two_factor.rs
+++ b/src/api/core/two_factor.rs
@@ -254,6 +254,29 @@ struct EnableU2FData {
     DeviceResponse: String,
 }
 
+// This struct is copied from the U2F lib
+// because challenge is not always sent
+#[derive(Deserialize)]
+#[serde(rename_all = "camelCase")]
+struct RegisterResponseCopy {
+    pub registration_data: String,
+    pub version: String,
+    pub challenge: Option<String>,
+    pub error_code: Option<NumberOrString>,
+    pub client_data: String,
+}
+
+impl RegisterResponseCopy {
+    fn into_response(self, challenge: String) -> RegisterResponse {
+        RegisterResponse {
+            registration_data: self.registration_data,
+            version: self.version,
+            challenge: challenge,
+            client_data: self.client_data,
+        }
+    }
+}
+
 #[post("/two-factor/u2f", data = "<data>")]
 fn activate_u2f(data: JsonUpcase<EnableU2FData>, headers: Headers, conn: DbConn) -> JsonResult {
     let data: EnableU2FData = data.into_inner().data;
@@ -278,8 +301,19 @@ fn activate_u2f(data: JsonUpcase<EnableU2FData>, headers: Headers, conn: DbConn)
 
         println!("RegisterResponse {:#?}", &data.DeviceResponse);
 
-        let response: RegisterResponse =
-            serde_json::from_str(&data.DeviceResponse).expect("Can't parse DeviceResponse data");
+        let response_copy: RegisterResponseCopy =
+            serde_json::from_str(&data.DeviceResponse).expect("Can't parse RegisterResponse data");
+
+        let error_code = response_copy
+            .error_code
+            .clone()
+            .map_or("0".into(), NumberOrString::into_string);
+
+        if error_code != "0" {
+            err!("Error registering U2F token")
+        }
+
+        let response = response_copy.into_response(challenge.challenge.clone());
 
         match U2F.register_response(challenge.clone(), response) {
             Ok(registration) => {
@@ -337,7 +371,7 @@ fn _create_u2f_challenge(user_uuid: &str, type_: TwoFactorType, conn: &DbConn) -
 // because it doesn't implement Deserialize
 #[derive(Serialize, Deserialize, Clone)]
 #[serde(rename_all = "camelCase")]
-pub struct RegistrationCopy {
+struct RegistrationCopy {
     pub key_handle: Vec<u8>,
     pub pub_key: Vec<u8>,
     pub attestation_cert: Option<Vec<u8>>,
diff --git a/src/api/mod.rs b/src/api/mod.rs
index 657b3e8..15f6778 100644
--- a/src/api/mod.rs
+++ b/src/api/mod.rs
@@ -26,7 +26,7 @@ struct PasswordData {
     MasterPasswordHash: String
 }
 
-#[derive(Deserialize, Debug)]
+#[derive(Deserialize, Debug, Clone)]
 #[serde(untagged)]
 enum NumberOrString {
     Number(i32),