diff --git a/changelog.d/13819.misc b/changelog.d/13819.misc
new file mode 100644
index 000000000..e2f3bc1f4
--- /dev/null
+++ b/changelog.d/13819.misc
@@ -0,0 +1 @@
+complement: init postgres DB directly inside the target image instead of the base postgres image to fix building using Buildah.
diff --git a/docker/complement/Dockerfile b/docker/complement/Dockerfile
index 3cfff19f9..0e13722d1 100644
--- a/docker/complement/Dockerfile
+++ b/docker/complement/Dockerfile
@@ -17,26 +17,24 @@ ARG SYNAPSE_VERSION=latest
 # the same debian version as Synapse's docker image (so the versions of the
 # shared libraries match).
 
-FROM postgres:13-bullseye AS postgres_base
-    # initialise the database cluster in /var/lib/postgresql
-    RUN gosu postgres initdb --locale=C --encoding=UTF-8 --auth-host password
-
-    # Configure a password and create a database for Synapse
-    RUN echo "ALTER USER postgres PASSWORD 'somesecret'" | gosu postgres postgres --single
-    RUN echo "CREATE DATABASE synapse" | gosu postgres postgres --single
-
 # now build the final image, based on the Synapse image.
 
 FROM matrixdotorg/synapse-workers:$SYNAPSE_VERSION
     # copy the postgres installation over from the image we built above
     RUN adduser --system --uid 999 postgres --home /var/lib/postgresql
-    COPY --from=postgres_base /var/lib/postgresql /var/lib/postgresql
-    COPY --from=postgres_base /usr/lib/postgresql /usr/lib/postgresql
-    COPY --from=postgres_base /usr/share/postgresql /usr/share/postgresql
+    COPY --from=postgres:13-bullseye /usr/lib/postgresql /usr/lib/postgresql
+    COPY --from=postgres:13-bullseye /usr/share/postgresql /usr/share/postgresql
     RUN mkdir /var/run/postgresql && chown postgres /var/run/postgresql
     ENV PATH="${PATH}:/usr/lib/postgresql/13/bin"
     ENV PGDATA=/var/lib/postgresql/data
 
+    # initialise the database cluster in /var/lib/postgresql
+    RUN gosu postgres initdb --locale=C --encoding=UTF-8 --auth-host password
+
+    # Configure a password and create a database for Synapse
+    RUN echo "ALTER USER postgres PASSWORD 'somesecret'" | gosu postgres postgres --single
+    RUN echo "CREATE DATABASE synapse" | gosu postgres postgres --single
+
     # Extend the shared homeserver config to disable rate-limiting,
     # set Complement's static shared secret, enable registration, amongst other
     # tweaks to get Synapse ready for testing.