diff --git a/pika-build-config/lto.sh b/pika-build-config/lto.sh
index c92b81ec9..761f36976 100644
--- a/pika-build-config/lto.sh
+++ b/pika-build-config/lto.sh
@@ -1,5 +1,5 @@
-export PIKA_PACKAGE_VERSION="3.9.0-1"
-export PIKA_PACKAGE_NAME="mpl-sphinx-theme"
+export PIKA_PACKAGE_VERSION="6.1-2"
+export PIKA_PACKAGE_NAME="python-btrees"
 export PIKA_PACKAGE_PATCH=false
 export PIKA_REBUILD=false
 export PIKA_REBUILD_VERSION="b0"