diff --git a/.docker/Dockerfile b/.docker/Dockerfile
index 1a674a160f4f665419edd48466c47e65c3a5836c..aac81f4399c05ffecf4163c33cab8f50b704f6ff 100644
--- a/.docker/Dockerfile
+++ b/.docker/Dockerfile
@@ -11,7 +11,7 @@ RUN apt-get install -y python3-pip
 COPY doc/requirements.txt requirements.txt
 RUN pip3 install -r requirements.txt
 
-RUN echo "deb ftp.de.debian.org/debian buster-backports main" > /etc/apt/sources.list.d/buster-backports.list
+RUN echo "deb http://ftp.de.debian.org/debian buster-backports main" > /etc/apt/sources.list.d/buster-backports.list
 RUN apt-get update
 RUN apt-get install -y cmake=3.16.3-3~bpo10+1