diff --git a/tests/test_seo.py b/tests/test_seo.py
index 47975801..eb6e7717 100644
--- a/tests/test_seo.py
+++ b/tests/test_seo.py
@@ -55,7 +55,8 @@ def test_legacy_redirects_keep_individual_targets_across_new_stable(self):
         (self.site / "versions.json").write_text(
             json.dumps(self.catalog), encoding="utf-8")
         self.page("index.html", '<div id="main-content"></div>')
-        with patch("versioning.build.version_overview", return_value=self.page("index.html").read_text()):
+        with patch.dict("os.environ", {"LIBRESIGN_DOC_BASE_PATH": ""}), \
+             patch("versioning.build.version_overview", return_value=self.page("index.html").read_text()):
             legacy_redirects(self.site, "15", routes={
                 "user_manual/index.html": "15/user_manual/index.html",
                 "user_manual/functionality.html": "main/user_manual/functionality.html",
@@ -64,6 +65,28 @@ def test_legacy_redirects_keep_individual_targets_across_new_stable(self):
         self.assertIn("url=/main/user_manual/functionality.html", redirect)
         self.assertNotIn("url=/15/user_manual/index.html", redirect)
 
+    def test_preview_legacy_routes_and_placeholder_are_not_indexable(self):
+        self.page("15/index.html")
+        self.page("main/user_manual/functionality.html")
+        self.page("index.html")
+        (self.site / "versions.json").write_text(json.dumps(self.catalog))
+        prefix = "/site-preview/docs-preview/pr-7"
+        with patch.dict("os.environ", {
+            "LIBRESIGN_DOC_BASE_PATH": prefix,
+            "LIBRESIGN_PREVIEW_PR": "7",
+        }), patch("versioning.build.version_overview",
+                 return_value=self.page("index.html").read_text()):
+            legacy_redirects(self.site, "15", routes={
+                "user_manual/functionality.html": "main/user_manual/functionality.html",
+            })
+            apply_seo(self.site, self.catalog, preview=True)
+
+        redirect = (self.site / "user_manual/functionality.html").read_text()
+        self.assertIn(f"url={prefix}/main/user_manual/functionality.html", redirect)
+        self.assertEqual(verify_seo(self.site, self.catalog, preview=True), [])
+        self.assertIn('name="robots" content="noindex,follow"',
+                      (self.site / "_review/index.html").read_text())
+
     def test_missing_redirect_destination_fails_before_deploy(self):
         self.page("15/index.html")
         (self.site / "versions.json").write_text(json.dumps(self.catalog))
diff --git a/versioning/build.py b/versioning/build.py
index 27683bce..f80eb910 100644
--- a/versioning/build.py
+++ b/versioning/build.py
@@ -162,10 +162,11 @@ def legacy_redirects(output: Path, current: str, *, routes: dict[str, str] | Non
         entry = output / "_review/index.html"
         entry.parent.mkdir(parents=True, exist_ok=True)
         entry.write_text(
-            "<!doctype html><html lang='en'><meta charset='utf-8'>"
-            "<title>Preview-only documentation</title>"
-            "<h1>Preview-only documentation</h1>"
-            "<p>Release-specific review pages are generated after validation.</p>",
+            "<!doctype html><html lang='en'><head><meta charset='utf-8'>"
+            "<title>Preview-only documentation</title></head><body>"
+            "<main><h1>Preview-only documentation</h1>"
+            "<p>Release-specific review pages are generated after validation.</p>"
+            "</main></body></html>",
             encoding="utf-8",
         )
     # The previous unversioned URLs are a permanent migration interface.