diff --git a/core/site_optimizer.go b/core/site_optimizer.go
index 1e4b01d89..f17122ce9 100644
--- a/core/site_optimizer.go
+++ b/core/site_optimizer.go
@@ -219,11 +219,11 @@ func (site *Site) optimizerUpdate(battery []measurement) error {
 
 			if ts := lp.EffectivePlanTime(); !ts.IsZero() {
 				// TODO precise slot placement
-				if slot := int(time.Until(ts) / tariff.SlotDuration); slot < minLen {
+				if slot := int(time.Until(ts) / tariff.SlotDuration); slot < minLen && slot >= 0 {
 					bat.SGoal = lo.RepeatBy(minLen, func(_ int) float32 { return 0 })
 					bat.SGoal[slot] = float32(goal)
 				} else {
-					site.log.DEBUG.Printf("plan beyond forecast range: %.1f at %v", goal, ts.Round(time.Minute))
+					site.log.DEBUG.Printf("plan beyond forecast range or overrun: %.1f at %v slot %d", goal, ts.Round(time.Minute), slot)
 				}
 			}