diff --git a/site/checks.mjs b/site/checks.mjs
index 8c98786..56d1365 100644
--- a/site/checks.mjs
+++ b/site/checks.mjs
@@ -1063,8 +1063,16 @@ export function checkPreviewField(rel, meta) {
   if (meta.preview === undefined || meta.preview === null || meta.preview === "") return [];
   const v = String(meta.preview);
   if (v === "none") return [];
-  if (/^https:\/\/\S+$/.test(v) && safeImageUrl(v) === new URL(v).href) return [];
-  if (/^https:\/\/\S+$/.test(v)) return [`${rel} preview must be an https:// image URL on a public host`];
+  if (/^https:\/\/\S+$/.test(v)) {
+    let href = null;
+    try {
+      href = new URL(v).href;
+    } catch {
+      href = null;
+    }
+    if (href !== null && safeImageUrl(v) === href) return [];
+    return [`${rel} preview must be an https:// image URL on a public host`];
+  }
   return [`${rel} preview must be "none" or an https:// image URL`];
 }
 
diff --git a/site/checks.test.mjs b/site/checks.test.mjs
index 9f11841..f6ccdf6 100644
--- a/site/checks.test.mjs
+++ b/site/checks.test.mjs
@@ -828,6 +828,8 @@ accepts("preview field: https url", checkPreviewField("ok.md", { preview: "https
 rejects("preview field: http refused", checkPreviewField("bad.md", { preview: "http://a/b.png" }), 'bad.md preview must be "none" or an https:// image URL');
 rejects("preview field: loopback refused", checkPreviewField("bad.md", { preview: "https://127.0.0.1/a.png" }), "bad.md preview must be an https:// image URL on a public host");
 rejects("preview field: word refused", checkPreviewField("bad.md", { preview: "yes" }), 'bad.md preview must be "none" or an https:// image URL');
+rejects("preview field: unparseable https url refused", checkPreviewField("bad.md", { preview: "https://[bad" }), "bad.md preview must be an https:// image URL on a public host");
+rejects("preview field: userinfo refused", checkPreviewField("bad.md", { preview: "https://u:p@a.example/b.png" }), "bad.md preview must be an https:// image URL on a public host");
 
 /* V30: line endings ------------------------------------------------------ */
 accepts("V30 accepts LF-only text", checkLineEndings("ok.md", "---\nid: a\n---\n\nBody\n"));