diff --git a/rules/manager.go b/rules/manager.go
index 4a001a9e8c0f9f5f56434d2b1953efce06661480..f901d8c5694e989bf02af45be10d510fdc5bfce2 100644
--- a/rules/manager.go
+++ b/rules/manager.go
@@ -369,7 +369,7 @@ func (g *Group) GetEvaluationDuration() time.Duration {
 
 // setEvaluationDuration sets the time in seconds the last evaluation took.
 func (g *Group) setEvaluationDuration(dur time.Duration) {
-	g.metrics.groupLastDuration.WithLabelValues(groupKey(g.file, g.name)).Set(float64(dur))
+	g.metrics.groupLastDuration.WithLabelValues(groupKey(g.file, g.name)).Set(dur.Seconds())
 
 	g.mtx.Lock()
 	defer g.mtx.Unlock()