diff --git a/README.md b/README.md
index d49185f..86eccaa 100644
--- a/README.md
+++ b/README.md
@@ -11,16 +11,16 @@ tested with [podman](https://podman.io/) and [Docker](https://www.docker.com).
   eagerly optimized for size, as it goal is to include all tools that are required for
   running Isabelle and tools based on Isabelle (e.g., HOL-TestGen). The following 
   versions are available on docker hub:
-      * [logicalhacking/debian4isabelle](https://hub.docker.com/r/logicalhacking/debian4isabelle)
+    * [logicalhacking/debian4isabelle](https://hub.docker.com/r/logicalhacking/debian4isabelle)
 
 * [isabelle](isabelle/Dockerfile) provides a parametrized Dockerfile to generate docker
   images for various version of Isabelle. The image will also contain a copy of the most
   recent version of the [AFP](https://www.isa-afp.org) available for the specified
   version of Isabelle. The following versions are available on docker hub:
-      * [logicalhacking/isabelle2020](https://hub.docker.com/r/logicalhacking/isabelle2020)
-      * [logicalhacking/isabelle2019](https://hub.docker.com/r/logicalhacking/isabelle2019)
-      * [logicalhacking/isabelle2018](https://hub.docker.com/r/logicalhacking/isabelle2018)
-      * [logicalhacking/isabelle2017](https://hub.docker.com/r/logicalhacking/isabelle2017)
+    * [logicalhacking/isabelle2020](https://hub.docker.com/r/logicalhacking/isabelle2020)
+    * [logicalhacking/isabelle2019](https://hub.docker.com/r/logicalhacking/isabelle2019)
+    * [logicalhacking/isabelle2018](https://hub.docker.com/r/logicalhacking/isabelle2018)
+    * [logicalhacking/isabelle2017](https://hub.docker.com/r/logicalhacking/isabelle2017)
 
 * [isabelle_dof](isabelle_dof/Dockerfile) provides a parametrized Dockerfile to generate
   docker images of [Isabelle/DOF](https://git.logicalhacking.com/isabelle_dof/isabelle_dof).