diff --git a/slides/index.yaml b/slides/index.yaml
index c98a0d1a..788d3b1f 100644
--- a/slides/index.yaml
+++ b/slides/index.yaml
@@ -5,6 +5,7 @@
   speaker: jpetazzo
   title: Deploying and scaling applications with Kubernetes
   attend: https://conferences.oreilly.com/velocity/vl-eu/public/schedule/detail/79109
+  slides: https://velocity-2019-11.container.training/
 
 - date: 2019-11-13
   country: fr
diff --git a/slides/kube-twodays.yml b/slides/kube-twodays.yml
index b2b13c15..73b0ace6 100644
--- a/slides/kube-twodays.yml
+++ b/slides/kube-twodays.yml
@@ -11,6 +11,8 @@ gitrepo: github.com/jpetazzo/container.training
 
 slides: http://velocity-2019-11.container.training/
 
+#slidenumberprefix: "#SomeHashTag — "
+
 exclude:
 - self-paced
 
diff --git a/slides/markmaker.py b/slides/markmaker.py
index dd50291f..37cbf6bc 100755
--- a/slides/markmaker.py
+++ b/slides/markmaker.py
@@ -80,7 +80,7 @@ def flatten(titles):
 
 
 def generatefromyaml(manifest, filename):
-    manifest = yaml.load(manifest)
+    manifest = yaml.safe_load(manifest)
 
     markdown, titles = processchapter(manifest["chapters"], filename)
     logging.debug("Found {} titles.".format(len(titles)))
@@ -111,6 +111,7 @@ def generatefromyaml(manifest, filename):
     html = html.replace("@@GITREPO@@", manifest["gitrepo"])
     html = html.replace("@@SLIDES@@", manifest["slides"])
     html = html.replace("@@TITLE@@", manifest["title"].replace("\n", " "))
+    html = html.replace("@@SLIDENUMBERPREFIX@@", manifest.get("slidenumberprefix", ""))
     return html
 
 
diff --git a/slides/workshop.html b/slides/workshop.html
index ffb378ce..96f56b04 100644
--- a/slides/workshop.html
+++ b/slides/workshop.html
@@ -28,6 +28,7 @@
       var slideshow = remark.create({
         ratio: '16:9',
         highlightSpans: true,
+        slideNumberFormat: '@@SLIDENUMBERPREFIX@@%current%/%total%',
         excludedClasses: [@@EXCLUDE@@]
       });
     </script>