diff --git a/packages/common/src/URN.js b/packages/common/src/URN.js
index 4366029..74407c9 100644
--- a/packages/common/src/URN.js
+++ b/packages/common/src/URN.js
@@ -7,6 +7,8 @@ export default class URN {
     this.nss = null;
     this.textGroup = null;
     this.work = null;
+    this.versionPart = null;
+    this.workPart = null;
     this.reference = null;
     this.version = null;
     this.destructureUrn();
@@ -16,18 +18,19 @@ export default class URN {
   destructureUrn() {
     const split = this.absolute.split(this.delimiter);
     [this.scheme, this.nid, this.nss, this.work, this.reference] = split;
-    this.version = `${this.scheme}:${this.nid}:${this.nss}:${this.work}:`;
-    // eslint-disable-next-line prefer-destructuring
-    this.textGroup = this.version
-      .split('.')[0]
-      .split(':')
-      .slice(-1)[0];
+    this.version = `${this.urnPrefix}:${this.work}:`;
+    const versionParts = this.version.split(':').slice(-2)[0].split('.');
+    [this.textGroup, this.workPart, this.versionPart] = versionParts;
   }
 
   toString() {
     return this.absolute;
   }
 
+  get urnPrefix() {
+    return `${this.scheme}:${this.nid}:${this.nss}`;
+  }
+
   get lcp() {
     return this.reference
       ? this.reference
@@ -36,4 +39,26 @@ export default class URN {
           .slice(-1)[0]
       : null;
   }
+
+  upTo(segment) {
+    // NOTE: Backported from https://github.com/scaife-viewer/scaife-viewer/blob/59fbb4eb6bd886285eb27bf95c5ea0ce578f2b3e/static/src/js/urn.js#L32C1-L49C4
+    const segments = [this.urnPrefix, ':'];
+    if (segment === 'textGroup') {
+      segments.push(this.textGroup, ':');
+      return segments.join('');
+    }
+    if (segment === 'work') {
+      segments.push(this.textGroup, '.');
+      segments.push(this.workPart, ':');
+      return segments.join('');
+    }
+    if (segment === 'version') {
+      return this.version
+    }
+    if (segment === 'reference')  {
+      return this.absolute;
+    }
+    return null;
+  }
+
 }
diff --git a/packages/widget-toc/src/TOCWidget.vue b/packages/widget-toc/src/TOCWidget.vue
index 36552d6..17a6639 100644
--- a/packages/widget-toc/src/TOCWidget.vue
+++ b/packages/widget-toc/src/TOCWidget.vue
@@ -76,15 +76,7 @@
     },
     computed: {
       passageWork() {
-        // FIXME: Fix this so we have "upTo" in URN module
-        if (this.passage) {
-          const [tgPart, workPart, ] = `${this.passage}`
-            .split(`${this.passage.nss}:`)[1]
-            .split(':')[0]
-            .split('.');
-          return `urn:cts:${this.passage.nss}:${tgPart}.${workPart}:`;
-        }
-        return '';
+        return this.passage ? this.passage.upTo('work') : '';
       },
       emptyMessage() {
         return SHOW_RELEVANT_ONLY