diff --git a/data/grid5000/sites/toulouse/clusters/montcalm/montcalm.json b/data/grid5000/sites/toulouse/clusters/montcalm/montcalm.json
index 03d76b995e7db724df4d17cb4aec27a9ce1ff72c..b778aab81307729cef218d260af9358b58f544e8 100644
--- a/data/grid5000/sites/toulouse/clusters/montcalm/montcalm.json
+++ b/data/grid5000/sites/toulouse/clusters/montcalm/montcalm.json
@@ -842,7 +842,8 @@
     {
       "description": "Default subset of metrics from Prometheus Node Exporter",
       "name": "prom_default_metrics",
-      "period": 15000,
+      "optional_period": 15000,
+      "period": 0,
       "source": {
         "id": [
           "node_boot_time_seconds",
diff --git a/input/grid5000/sites/toulouse/clusters/montcalm/montcalm_metrics.yaml b/input/grid5000/sites/toulouse/clusters/montcalm/montcalm_metrics.yaml
index d60f2903c6da291b2d802b636258ff5d35d92cd8..3e22d1c0e1da35decb765bd4eff3e91ced2b927b 100644
--- a/input/grid5000/sites/toulouse/clusters/montcalm/montcalm_metrics.yaml
+++ b/input/grid5000/sites/toulouse/clusters/montcalm/montcalm_metrics.yaml
@@ -582,7 +582,8 @@ metrics:
 
   - name: prom_default_metrics
     description: Default subset of metrics from Prometheus Node Exporter
-    period: 15000
+    period: 0
+    optional_period: 15000
     source:
       protocol: prometheus
       port: 9100