diff --git a/src/interfaces/IManifest.ts b/src/interfaces/IManifest.ts
index 7bdca8e..32ab0d7 100644
--- a/src/interfaces/IManifest.ts
+++ b/src/interfaces/IManifest.ts
@@ -1,16 +1,11 @@
+import IManifestRelease from './IManifestRelease';
+
 /** A patch manifest, containing a list of releases, how to patch them, and which one the current release is. */
 export default interface IManifest {
   /** Current release. */
   current: number;
   /** List of releases. */
   releases: {
-    [s: string]: {
-      /** SHA1 hash of this release. */
-      sha1: string;
-      /** List of releases from where we can patch to this release. */
-      from: number[];
-      /** List of releases that this release can be patched to. */
-      to: number[];
-  };
+    [s: string]: IManifestRelease;
 };
 }
diff --git a/src/interfaces/IManifestRelease.ts b/src/interfaces/IManifestRelease.ts
new file mode 100644
index 0000000..59115bd
--- /dev/null
+++ b/src/interfaces/IManifestRelease.ts
@@ -0,0 +1,8 @@
+export default interface IManifestRelease {
+  /** SHA1 hash of this release. */
+  sha1: string;
+  /** List of releases from where we can patch to this release. */
+  from: number[];
+  /** List of releases that this release can be patched to. */
+  to: number[];
+}
diff --git a/src/ssn/reader/parsePatchmanifest.ts b/src/ssn/reader/parsePatchmanifest.ts
index 0dac18d..d34d351 100644
--- a/src/ssn/reader/parsePatchmanifest.ts
+++ b/src/ssn/reader/parsePatchmanifest.ts
@@ -1,28 +1,44 @@
+import * as xmlJs from 'xml-js';
 import IManifest from '../../interfaces/IManifest';
+import IManifestRelease from '../../interfaces/IManifestRelease';
+
+/** Given an xmlJs element, returns the child elements, or an empty array if it has no children. */
+function getChildren(ele: xmlJs.Element): xmlJs.Element[] {
+  return ele.elements !== undefined ? ele.elements : [];
+}
+/** Given an xmlJs element, returns the child at the given index. Throws an error if that element does not exist. */
+function getChild(ele: xmlJs.Element, index: number): xmlJs.Element {
+  return (ele.elements as xmlJs.Element[])[index] as xmlJs.Element;
+}
+/** Given an xmlJs element, returns the text contents. */
+function getContent(ele: xmlJs.Element): string {
+  const childElements = getChildren(ele);
+  return (childElements.length > 0) ? String(childElements[0].text) : '';
+}
 
 /** Receives a JSON-converted version of the manifest.xml file, and returns an easier to read JSON file */
-export default function parsePatchManifest(manifestFile: any): IManifest {
+export default function parsePatchManifest(manifestFile: xmlJs.Element): IManifest {
   const out: IManifest = { current: -1, releases: {} };
 
-  const PatchManifest = manifestFile.elements[0];
+  const PatchManifest = getChild(manifestFile, 0);
 
   //<RequiredRelease>289</RequiredRelease>
-  const RequiredRelease = PatchManifest.elements[2];
-  out.current = Number(RequiredRelease.elements[0].text);
+  const RequiredRelease = getChild(PatchManifest, 2);
+  out.current = Number(getContent(RequiredRelease));
 
   //<Releases><Release><Id>0</Id><SHA1>53678f8057e52896a8145dca5c188ab3f24fa55f</SHA1></Release></Releases>
-  const Releases = PatchManifest.elements[7];
-  Releases.elements.forEach(function(Release: any) {
-    const id = Release.elements[0].elements[0].text;
-    const sha1 = Release.elements[1].elements[0].text;
+  const Releases = getChild(PatchManifest, 7);
+  getChildren(Releases).forEach(function(Release: xmlJs.Element) {
+    const id = getContent(getChild(Release, 0));
+    const sha1 = getContent(getChild(Release, 1));
     out.releases[id] = { sha1, from: [], to: [] };
   });
 
   //<ReleaseUpdatePaths><ReleaseUpdatePath><From>287</From><To>288</To><ExtraDataItem>...</ExtraDataItem></ReleaseUpdatePath></ReleaseUpdatePaths
-  const ReleaseUpdatePaths = PatchManifest.elements[8];
-  ReleaseUpdatePaths.elements.forEach(function(ReleaseUpdatePath: any) {
-    const from = ReleaseUpdatePath.elements[0].elements[0].text;
-    const to = ReleaseUpdatePath.elements[1].elements[0].text;
+  const ReleaseUpdatePaths = getChild(PatchManifest, 8);
+  getChildren(ReleaseUpdatePaths).forEach(function(ReleaseUpdatePath: xmlJs.Element) {
+    const from = getContent(getChild(ReleaseUpdatePath, 0));
+    const to = getContent(getChild(ReleaseUpdatePath, 1));
     //Release -1 does not exist but is a valid "from", e.g. for -1to0
     if (from !== '-1') {
       out.releases[from].to.push(Number(to));
@@ -30,5 +46,13 @@ export default function parsePatchManifest(manifestFile: any): IManifest {
     out.releases[to].from.push(Number(from));
   });
 
+  //freeze values to prevent modification
+  Object.values(out).forEach(function(entry: IManifestRelease) {
+    Object.freeze(entry.from);
+    Object.freeze(entry.to);
+    Object.freeze(entry);
+  });
+  Object.freeze(out);
+
   return out;
 }