diff --git a/NEWS.md b/NEWS.md
index e986b09ca..403ccefd5 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -1,5 +1,6 @@
 # pkgdown (development version)
 
+* Bootstrap 3 has been deprecated. It was superseded in Dec 2021, and now we're starting to more directly encourage folks to move away from it.
 * `build_home_index()` now renders math if you use it in your home page (#2263).
 * `build_home()` now correctly escapes special HTML characters in the bibtex citation (#2022).
 * BS5 templates no longer include empty link to logo when none exists (#2536).
diff --git a/R/check.R b/R/check.R
index ac4ceab03..69761135c 100644
--- a/R/check.R
+++ b/R/check.R
@@ -35,6 +35,13 @@ pkgdown_sitrep <- function(pkg = ".") {
   cli::cli_rule("Sitrep")
 
   pkg <- as_pkgdown(pkg)
+  if (pkg$bs_version == 3) {
+    cli::cli_inform(c(
+      x = "Bootstrap 3 is deprecated; please switch to Bootstrap 5.",
+      i = "Learn more at {.url https://www.tidyverse.org/blog/2021/12/pkgdown-2-0-0/#bootstrap-5}."
+    ))
+  }
+
   error_to_sitrep("URLs", check_urls(pkg))
   error_to_sitrep("Open graph metadata", data_open_graph(pkg))
   error_to_sitrep("Articles metadata", data_articles_index(pkg))
diff --git a/tests/testthat/_snaps/check.md b/tests/testthat/_snaps/check.md
index 08744c86d..52d533696 100644
--- a/tests/testthat/_snaps/check.md
+++ b/tests/testthat/_snaps/check.md
@@ -1,3 +1,16 @@
+# sitrep complains about BS3
+
+    Code
+      pkgdown_sitrep(pkg)
+    Message
+      -- Sitrep ----------------------------------------------------------------------
+      x Bootstrap 3 is deprecated; please switch to Bootstrap 5.
+      i Learn more at <https://www.tidyverse.org/blog/2021/12/pkgdown-2-0-0/#bootstrap-5>.
+      v URLs ok.
+      v Open graph metadata ok.
+      v Articles metadata ok.
+      v Reference metadata ok.
+
 # sitrep reports all problems
 
     Code
diff --git a/tests/testthat/test-check.R b/tests/testthat/test-check.R
index 4d451f1fa..7a09611d4 100644
--- a/tests/testthat/test-check.R
+++ b/tests/testthat/test-check.R
@@ -1,3 +1,11 @@
+test_that("sitrep complains about BS3", {
+  pkg <- local_pkgdown_site(test_path("assets/open-graph"), meta = "
+    template: 
+      bootstrap: 3
+  ")
+  expect_snapshot(pkgdown_sitrep(pkg))
+})
+
 test_that("sitrep reports all problems", {
   pkg <- local_pkgdown_site(test_path("assets/reference"), meta = "
     reference: