diff --git a/exim4/Dockerfile b/exim4/Dockerfile
index 81d4160642f62551c84fb635526fa499e005b62d..e6261c82c80199646e0a12ea1775902dc192643a 100644
--- a/exim4/Dockerfile
+++ b/exim4/Dockerfile
@@ -1,4 +1,4 @@
-FROM debian:buster-slim
+FROM debian:bullseye-slim
 # hadolint ignore=DL3008,DL4006
 RUN apt-get update && \
     DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommends \