diff --git a/lighthouse-core/report/html/renderer/details-renderer.js b/lighthouse-core/report/html/renderer/details-renderer.js
index 84a5d49f6cb8..5f5cd7910582 100644
--- a/lighthouse-core/report/html/renderer/details-renderer.js
+++ b/lighthouse-core/report/html/renderer/details-renderer.js
@@ -63,9 +63,9 @@ class DetailsRenderer {
         return null;
 
       default: {
-        // @ts-ignore tsc thinks this unreachable, but ts-ignore for error message just in case.
-        const detailsType = details.type;
-        throw new Error(`Unknown type: ${detailsType}`);
+        // @ts-ignore tsc thinks this is unreachable, but be forward compatible
+        // with new unexpected detail types.
+        return this._renderUnknown(details.type, details);
       }
     }
   }
@@ -188,6 +188,22 @@ class DetailsRenderer {
     return element;
   }
 
+  /**
+   * @param {string} type
+   * @param {*} value
+   */
+  _renderUnknown(type, value) {
+    // eslint-disable-next-line no-console
+    console.error(`Unknown details type: ${type}`, value);
+    const element = this._dom.createElement('details', 'lh-unknown');
+    this._dom.createChildOf(element, 'summary').textContent =
+      `We don't know how to render audit details of type \`${type}\`. ` +
+      'The Lighthouse version that collected this data is likely newer than the Lighthouse ' +
+      'version of the report renderer. Expand for the raw JSON.';
+    this._dom.createChildOf(element, 'pre').textContent = JSON.stringify(value, null, 2);
+    return element;
+  }
+
   /**
    * Render a details item value for embedding in a table. Renders the value
    * based on the heading's valueType, unless the value itself has a `type`
@@ -218,7 +234,7 @@ class DetailsRenderer {
           return this.renderTextURL(value.value);
         }
         default: {
-          throw new Error(`Unknown valueType: ${value.type}`);
+          return this._renderUnknown(value.type, value);
         }
       }
     }
@@ -267,7 +283,7 @@ class DetailsRenderer {
         }
       }
       default: {
-        throw new Error(`Unknown valueType: ${heading.valueType}`);
+        return this._renderUnknown(heading.valueType, value);
       }
     }
   }
diff --git a/lighthouse-core/report/html/report-styles.css b/lighthouse-core/report/html/report-styles.css
index 880c39b1659d..6116e483a17f 100644
--- a/lighthouse-core/report/html/report-styles.css
+++ b/lighthouse-core/report/html/report-styles.css
@@ -1391,6 +1391,11 @@
   display: block;
 }
 
+.lh-unknown pre {
+  overflow: scroll;
+  border: solid 1px var(--color-gray-200);
+}
+
 .lh-text__url > a {
   color: inherit;
   text-decoration: none;
diff --git a/lighthouse-core/test/report/html/renderer/details-renderer-test.js b/lighthouse-core/test/report/html/renderer/details-renderer-test.js
index ba7cf34c7dfd..27660ea05b8b 100644
--- a/lighthouse-core/test/report/html/renderer/details-renderer-test.js
+++ b/lighthouse-core/test/report/html/renderer/details-renderer-test.js
@@ -194,14 +194,18 @@ describe('DetailsRenderer', () => {
       assert.strictEqual(diagnosticEl, null);
     });
 
-    it('throws on unknown details type', () => {
+    it('renders an unknown details type', () => {
       // Disallowed by type system, but test that we get an error message out just in case.
       const details = {
         type: 'imaginary',
         items: 5,
       };
 
-      assert.throws(() => renderer.render(details), /^Error: Unknown type: imaginary$/);
+      const el = renderer.render(details);
+      const summaryEl = el.querySelector('summary');
+      expect(summaryEl.textContent)
+        .toContain('We don\'t know how to render audit details of type `imaginary`');
+      assert.strictEqual(el.lastChild.textContent, JSON.stringify(details, null, 2));
     });
   });
 
@@ -451,7 +455,7 @@ describe('DetailsRenderer', () => {
       assert.strictEqual(codeItemEl.innerHTML, '<pre class="lh-code">invalid-url://example.com/</pre>');
     });
 
-    it('throws on unknown heading itemType', () => {
+    it('renders an unknown heading itemType', () => {
       // Disallowed by type system, but test that we get an error message out just in case.
       const details = {
         type: 'table',
@@ -459,10 +463,15 @@ describe('DetailsRenderer', () => {
         items: [{content: 'some string'}],
       };
 
-      assert.throws(() => renderer.render(details), /^Error: Unknown valueType: notRealValueType$/);
+      const el = renderer.render(details);
+      const unknownEl = el.querySelector('td.lh-table-column--notRealValueType .lh-unknown');
+      const summaryEl = unknownEl.querySelector('summary');
+      expect(summaryEl.textContent)
+        .toContain('We don\'t know how to render audit details of type `notRealValueType`');
+      assert.strictEqual(unknownEl.lastChild.textContent, '"some string"');
     });
 
-    it('throws on unknown item object type', () => {
+    it('renders an unknown item object type', () => {
       // Disallowed by type system, but test that we get an error message out just in case.
       const item = {
         type: 'imaginaryItem',
@@ -475,7 +484,12 @@ describe('DetailsRenderer', () => {
         items: [{content: item}],
       };
 
-      assert.throws(() => renderer.render(details), /^Error: Unknown valueType: imaginaryItem$/);
+      const el = renderer.render(details);
+      const unknownEl = el.querySelector('td.lh-table-column--url .lh-unknown');
+      const summaryEl = unknownEl.querySelector('summary');
+      expect(summaryEl.textContent)
+        .toContain('We don\'t know how to render audit details of type `imaginaryItem`');
+      assert.strictEqual(unknownEl.lastChild.textContent, JSON.stringify(item, null, 2));
     });
 
     it('uses the item\'s type over the heading type', () => {