diff --git a/platform-independent/c/core/Dockerfile b/Dockerfile
similarity index 69%
rename from platform-independent/c/core/Dockerfile
rename to Dockerfile
index c5d8ed6b..1b7fa59e 100644
--- a/platform-independent/c/core/Dockerfile
+++ b/Dockerfile
@@ -1,3 +1,6 @@
+# Set up a container for doing gradle cross-compiling.
+#
+# docker build -t lhunath/mp-gradle --file Dockerfile /var/empty
 FROM debian:stable-slim
 
 # https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=863199
@@ -6,4 +9,4 @@ RUN mkdir -p /usr/share/man/man1
 RUN apt-get update && apt-get install -y default-jdk-headless git-core bash libtool automake autoconf make g++-multilib
 RUN git clone --depth=3 $(: --shallow-submodules) --recurse-submodules --branch rewrite https://gitlab.com/MasterPassword/MasterPassword.git /mpw
 RUN cd /mpw && ./gradlew -i clean
-#RUN cd /mpw && git pull && git log -1 && ./gradlew -i check
+RUN cd /mpw && git pull && git log -1 && ./gradlew -i check