diff --git a/testing/testing.conf b/testing/testing.conf
index 8a506aad3..b2348ad2e 100644
--- a/testing/testing.conf
+++ b/testing/testing.conf
@@ -49,7 +49,7 @@ fi
 # Base image settings
 # The base image is a pristine OS installation created using debootstrap.
 : ${BASEIMGSIZE=2500}
-: ${BASEIMGSUITE=bullseye}
+: ${BASEIMGSUITE=bookworm}
 : ${BASEIMGARCH=amd64}
 : ${BASEIMG=$IMGDIR/debian-$BASEIMGSUITE-$BASEIMGARCH.$IMGEXT}
 : ${BASEIMGMIRROR=http://http.debian.net/debian}