diff --git a/src/main/resources/challenges/challenge-51/Dockerfile_challenge51 b/src/main/resources/challenges/challenge-51/Dockerfile_challenge51
index e86bc97d4..06dab2f29 100644
--- a/src/main/resources/challenges/challenge-51/Dockerfile_challenge51
+++ b/src/main/resources/challenges/challenge-51/Dockerfile_challenge51
@@ -1,4 +1,4 @@
-# syntax=docker/dockerfile:1.20
+# syntax=docker/dockerfile:1.21
 FROM debian:stable-slim
 
 RUN --mount=type=secret,id=db_user \