diff --git a/.github/workflows/build-push-image-commit.yaml b/.github/workflows/build-push-image-commit.yaml
index b998620..9823973 100644
--- a/.github/workflows/build-push-image-commit.yaml
+++ b/.github/workflows/build-push-image-commit.yaml
@@ -58,6 +58,7 @@ jobs:
           # so all contents put in /home/jovyan are lost. This particularly prevents any 'start' script from
           # working, as it is needed in runtime.
           REPO_DIR: /srv/repo
+          APPENDIX_FILE: Dockerfile.appendix
 
       # Lets us monitor disks getting full as images get bigger over time
       - name: Show how much disk space is left
diff --git a/.github/workflows/build-test-image.yaml b/.github/workflows/build-test-image.yaml
index 097baa7..c10e0ec 100644
--- a/.github/workflows/build-test-image.yaml
+++ b/.github/workflows/build-test-image.yaml
@@ -43,6 +43,7 @@ jobs:
           FORCE_REPO2DOCKER_VERSION: jupyter-repo2docker==2024.07.0
           REPO_DIR: /srv/repo
           NO_PUSH: true
+          APPENDIX_FILE: Dockerfile.appendix
 
       # Lets us monitor disks getting full as images get bigger over time
       - name: Show how much disk space is left
diff --git a/Dockerfile.appendix b/Dockerfile.appendix
new file mode 100644
index 0000000..ebaadb4
--- /dev/null
+++ b/Dockerfile.appendix
@@ -0,0 +1,11 @@
+USER root
+
+# As requested in slack.
+# http://www.dcc.fc.up.pt/gtries/
+# https://github.com/ComplexNetworks-DCC-FCUP/gtrieScanner
+RUN wget -O /tmp/gtrieScanner.zip https://www.dcc.fc.up.pt/gtries/gtrieScanner_src_01.zip && \
+    unzip -d /tmp /tmp/gtrieScanner.zip && \
+    make -C /tmp/gtrieScanner_src_01 && \
+    install -o root -g root -m 0755 /tmp/gtrieScanner_src_01/gtrieScanner /usr/local/bin/
+
+USER $NB_USER
diff --git a/postBuild b/postBuild
index 1b6bcc9..539a223 100644
--- a/postBuild
+++ b/postBuild
@@ -1,5 +1,7 @@
 #!/usr/bin/env bash
 
+set -e
+
 # installing chromium browser to enable webpdf conversion using nbconvert
 export PLAYWRIGHT_BROWSERS_PATH=${CONDA_DIR}
 playwright install chromium