diff --git a/build.sh b/build.sh
index d5bade9..66bf894 100755
--- a/build.sh
+++ b/build.sh
@@ -6,6 +6,12 @@ set -euo pipefail
 PATH="/tmp/claat:${PATH}" python3 ./build.py
 
 sed -e 's#https://storage.googleapis.com/claat-public#/static#g' -i build/*/index.html
+# Stop focus() inside an embedding iframe from scrolling the parent page (see static/iframe-focus-fix.js)
+sed -e 's#<script src="/static/codelab-elements.js"></script>#<script src="/static/iframe-focus-fix.js"></script>&#' -i build/*/index.html
+if grep -L 'iframe-focus-fix.js' build/*/index.html | grep -q .; then
+  echo "iframe-focus-fix.js was not injected into every page - has claat's script tag changed?" >&2
+  exit 1
+fi
 
 # The public static hosting seems offline (e.g. https://storage.googleapis.com/claat-public/codelab-elements.css) so we vendor these assets:
 # Built by running `USE_BAZEL_VERSION=0.19.1 bazel build :bundle` with patches to:
diff --git a/static/iframe-focus-fix.js b/static/iframe-focus-fix.js
new file mode 100644
index 0000000..7237d37
--- /dev/null
+++ b/static/iframe-focus-fix.js
@@ -0,0 +1,13 @@
+// When a codelab is embedded in an iframe (e.g. on the CYF curriculum site),
+// codelab-elements.js focuses the current step on load. Focusing an element
+// inside an iframe scrolls the parent page to the iframe, losing the reader's
+// place. Force preventScroll on every focus() call, only when embedded.
+// Must load before codelab-elements.js.
+(function () {
+  if (window.self === window.top) return;
+  var originalFocus = HTMLElement.prototype.focus;
+  HTMLElement.prototype.focus = function (options) {
+    var opts = Object.assign({}, options, { preventScroll: true });
+    return originalFocus.call(this, opts);
+  };
+})();