diff --git a/app/client/models/gristUrlState.ts b/app/client/models/gristUrlState.ts
index 1d9fa247..4c5c3b15 100644
--- a/app/client/models/gristUrlState.ts
+++ b/app/client/models/gristUrlState.ts
@@ -224,7 +224,7 @@ export class UrlStateImpl {
 
 /**
  * Given value like `foo bar baz`, constructs URL by checking if `baz` is a valid URL and,
- * if not, prepending `http://`.
+ * if not, prepending `https://`.
  */
 export function constructUrl(value: CellValue): string {
   if (typeof value !== 'string') {
@@ -235,8 +235,8 @@ export function constructUrl(value: CellValue): string {
     // Try to construct a valid URL
     return (new URL(url)).toString();
   } catch (e) {
-    // Not a valid URL, so try to prefix it with http
-    return 'http://' + url;
+    // Not a valid URL, so try to prefix it with https
+    return 'https://' + url;
   }
 }
 
diff --git a/app/client/ui/MarkdownCellRenderer.ts b/app/client/ui/MarkdownCellRenderer.ts
index 036572ff..4151a65b 100644
--- a/app/client/ui/MarkdownCellRenderer.ts
+++ b/app/client/ui/MarkdownCellRenderer.ts
@@ -1,10 +1,11 @@
+import {constructUrl} from 'app/client/models/gristUrlState';
 import {gristIconLink} from 'app/client/ui2018/links';
 import escape from 'lodash/escape';
 import {marked} from 'marked';
 
 export const renderer = new marked.Renderer();
 
-renderer.link = ({href, text}) => gristIconLink(href, text).outerHTML;
+renderer.link = ({href, text}) => gristIconLink(constructUrl(href), text).outerHTML;
 
 // Disable Markdown features that we aren't ready to support yet.
 renderer.hr = ({raw}) => raw;