diff --git a/Dockerfile b/Dockerfile
index aadcf20..354c85c 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,21 +1,26 @@
 # This Dockerfile can be used to create a Docker image/container
 # that runs the unit tests on the LinkTitles extension.
-FROM mediawiki:1.34
-MAINTAINER Daniel Kraus (https://www.bovender.de)
-RUN apt update -yqq && \
-    apt install -yqq \
-	php7.0-sqlite \
+FROM mediawiki:1.35
+LABEL "MAINTAINER" Daniel Kraus (https://www.bovender.de)
+RUN apt-get update -yqq && \
+	apt-get install -yqq \
+	php7.3-sqlite \
 	sqlite3 \
 	unzip \
 	zip
-RUN curl https://raw.githubusercontent.com/composer/getcomposer.org/cb19f2aa3aeaa2006c0cd69a7ef011eb31463067/web/installer -s | php -- --quiet
-RUN php composer.phar install
+
+WORKDIR /var/www/html
+ADD install-composer.sh install-composer.sh
+RUN chmod +x install-composer.sh
+RUN ./install-composer.sh
 
 COPY . /var/www/html/extensions/LinkTitles/
 RUN mkdir /data && chown www-data /data
 
+RUN php composer.phar update
+
 WORKDIR /var/www/html/maintenance
-RUN php install.php --pass admin --dbtype sqlite --extensions LinkTitles Tests admin
+RUN php install.php --pass linktitles --dbtype sqlite --extensions LinkTitles Tests admin
 
 WORKDIR /var/www/html/tests/phpunit
 CMD ["php", "phpunit.php", "--group", "bovender"]
diff --git a/install-composer.sh b/install-composer.sh
new file mode 100644
index 0000000..9aa0c1f
--- /dev/null
+++ b/install-composer.sh
@@ -0,0 +1,22 @@
+#!/bin/sh
+
+# This is a slightly modified version of the installer script published at
+# https://getcomposer.org/doc/faqs/how-to-install-composer-programmatically.md
+# It does not depend on `wget` and uses `curl` instead.
+
+EXPECTED_CHECKSUM="$(curl -q https://composer.github.io/installer.sig)"
+php -r "copy('https://getcomposer.org/installer', 'composer-setup.php');"
+ACTUAL_CHECKSUM="$(php -r "echo hash_file('sha384', 'composer-setup.php');")"
+
+if [ "$EXPECTED_CHECKSUM" != "$ACTUAL_CHECKSUM" ]
+then
+    >&2 echo 'ERROR: Invalid installer checksum'
+    rm composer-setup.php
+    exit 1
+fi
+
+# May need to remove the explicit pinning of version 1 in the future
+php composer-setup.php --quiet --1
+RESULT=$?
+rm composer-setup.php
+exit $RESULT