diff --git a/flake.nix b/flake.nix
index 1ed812b..1b9b626 100644
--- a/flake.nix
+++ b/flake.nix
@@ -111,6 +111,14 @@
           '';
         };
         invtracker-docs = pkgs.callPackage ./doc.nix { inherit self texlive-env; };
+        invtracker-web = pkgs.mkYarnPackage rec {
+          pname = "invtracker-web";
+          version = self.lastModifiedDate;
+          src = "${self}/map-desktop";
+          yarnLock = "${self}/map-desktop/yarn.lock";
+          buildPhase = "yarn run build";
+          installPhase = "cp -rv dist $out";
+        };
       };
 
       hydraJobs =
diff --git a/map-desktop/src/api/listItems.ts b/map-desktop/src/api/listItems.ts
index 5a4db7c..e045c69 100644
--- a/map-desktop/src/api/listItems.ts
+++ b/map-desktop/src/api/listItems.ts
@@ -23,7 +23,8 @@ export class GeoLocation {
     }
     const longitude = parseFloat(longitudeString);
     const altitudeNode = node.getElementsByTagName('alt')[0];
-    const altitude = altitudeNode !== undefined ? parseFloat(altitudeNode.textContent) : null;
+    const altitudeText = altitudeNode === null ? null : altitudeNode.textContent;
+    const altitude = altitudeText !== null ? parseFloat(altitudeText) : null;
     const timeString = node.getElementsByTagName('time')[0].textContent;
     if (timeString === null) {
       throw new Error('Missing time');
@@ -54,7 +55,8 @@ export class TrackedItem {
     if (id === null) {
       throw new Error('Missing id');
     }
-    const nameNode = node.getElementsByTagName('name')[0].textContent;
+    const nameNode = node.getElementsByTagName('name')[0];
+    const name = nameNode === null ? null : nameNode.textContent;
     if (name === null) {
       throw new Error('Missing name');
     }