diff --git a/app/src/main/java/it/danieleverducci/lunatracker/MainActivity.kt b/app/src/main/java/it/danieleverducci/lunatracker/MainActivity.kt
index 2e7c051..9676733 100644
--- a/app/src/main/java/it/danieleverducci/lunatracker/MainActivity.kt
+++ b/app/src/main/java/it/danieleverducci/lunatracker/MainActivity.kt
@@ -890,12 +890,18 @@ class MainActivity : AppCompatActivity() {
                 )
                 picker.minValue = 1
                 picker.maxValue = if (isSleep) 180 else 60
+                val oldQuantity = event.quantity
                 picker.value = if (event.quantity > 0) Math.min(event.quantity, picker.maxValue) else if (isSleep) 30 else 15
 
                 pickerDialog.setTitle(if (isSleep) R.string.sleep_duration_title else R.string.breastfeeding_duration_title)
                 pickerDialog.setView(pickerView)
                 pickerDialog.setPositiveButton(android.R.string.ok) { _, _ ->
-                    event.quantity = picker.value
+                    val newQuantity = picker.value
+                    if (newQuantity != oldQuantity) {
+                        // Adjust end time based on duration change (duration reduced = end time earlier)
+                        event.time = event.time - (oldQuantity - newQuantity) * 60L
+                        event.quantity = newQuantity
+                    }
                     quantityTextView.text = NumericUtils(this@MainActivity).formatEventQuantity(event)
                     recyclerView.adapter?.notifyDataSetChanged()
                     saveLogbook()