diff --git a/.ci/isabelle4isadof/Dockerfile b/.ci/isabelle4isadof/Dockerfile
index 53aed5e..76039a8 100644
--- a/.ci/isabelle4isadof/Dockerfile
+++ b/.ci/isabelle4isadof/Dockerfile
@@ -24,7 +24,7 @@
 #
 # SPDX-License-Identifier: BSD-2-Clause
 
-FROM logicalhacking:isabelle2017
+FROM logicalhacking:isabelle2018
 
 WORKDIR /home/isabelle
 COPY thy_output.ML /home/isabelle/Isabelle/src/Pure/Thy