diff --git a/os/build.py b/os/build.py
index 8bae320..c84070d 100755
--- a/os/build.py
+++ b/os/build.py
@@ -165,6 +165,9 @@ def main():
         # so we need to copy them somewhere else and restore them after the install.
         for listpath in pathlib.Path('config/archives').glob('*.list.chroot'):
             run(["cp", str(listpath), f"config/includes.chroot/usr/local/share/target-sources/{listpath.name.removesuffix('.chroot')}"])
+        # Insert distribution into source configs.
+        for sourcepath in pathlib.Path('config/includes.chroot/usr/local/share/target-sources').glob('*'):
+            edit_file(sourcepath, lambda s: s.replace("@DISTRIBUTION@", DISTRIBUTION))
     elif args.variant == "contestant":
         # Insert root password into hook script.
         edit_file("config/hooks/live/2010-contestant.hook.chroot",
diff --git a/os/layers/training-installer/includes.chroot/usr/local/share/target-sources/debian.sources b/os/layers/training-installer/includes.chroot/usr/local/share/target-sources/debian.sources
index a7c1e88..fd89bcb 100644
--- a/os/layers/training-installer/includes.chroot/usr/local/share/target-sources/debian.sources
+++ b/os/layers/training-installer/includes.chroot/usr/local/share/target-sources/debian.sources
@@ -1,11 +1,11 @@
 Types: deb deb-src
 URIs: http://deb.debian.org/debian
-Suites: bookworm bookworm-updates
+Suites: @DISTRIBUTION@ @DISTRIBUTION@-updates
 Components: main contrib non-free non-free-firmware
 Signed-By: /usr/share/keyrings/debian-archive-keyring.gpg
 
 Types: deb deb-src
 URIs: http://deb.debian.org/debian-security
-Suites: bookworm-security
+Suites: @DISTRIBUTION@-security
 Components: main contrib non-free non-free-firmware
 Signed-By: /usr/share/keyrings/debian-archive-keyring.gpg