diff --git a/bundles/grafana/dashboard-rows/dovecot.py b/bundles/grafana/dashboard-rows/dovecot.py
index abc0af1..64405b7 100644
--- a/bundles/grafana/dashboard-rows/dovecot.py
+++ b/bundles/grafana/dashboard-rows/dovecot.py
@@ -168,6 +168,7 @@ def dashboard_row_dovecot(panel_id, node):
         r["_field"] == "read_bytes" and
         r["host"] == "{node.name}"
     )
+    |> derivative(unit: 1s)
     |> aggregateWindow(every: v.windowPeriod, fn: mean, createEmpty: false)
     |> yield(name: "read")""",
                         'resultFormat': 'time_series',
@@ -196,6 +197,7 @@ def dashboard_row_dovecot(panel_id, node):
             _value: r._value * -1
         }})
     )
+    |> derivative(unit: 1s)
     |> aggregateWindow(every: v.windowPeriod, fn: mean, createEmpty: false)
     |> yield(name: "write")""",
                         'resultFormat': 'time_series',