diff --git a/core/src/com/unciv/logic/city/CityInfo.kt b/core/src/com/unciv/logic/city/CityInfo.kt
index a3fce4e287..a146797d9a 100644
--- a/core/src/com/unciv/logic/city/CityInfo.kt
+++ b/core/src/com/unciv/logic/city/CityInfo.kt
@@ -326,6 +326,7 @@ class CityInfo {
         }
 
         isPuppet=false
+        cityConstructions.inProgressConstructions.clear() // undo all progress of the previous civ on units etc.
         cityStats.update()
         UncivGame.Current.worldScreen.shouldUpdate=true
     }
diff --git a/core/src/com/unciv/logic/map/MapUnit.kt b/core/src/com/unciv/logic/map/MapUnit.kt
index b4e4820545..ea62cc8720 100644
--- a/core/src/com/unciv/logic/map/MapUnit.kt
+++ b/core/src/com/unciv/logic/map/MapUnit.kt
@@ -238,6 +238,7 @@ class MapUnit {
             goldCostOfUpgrade = (goldCostOfUpgrade * 0.66f).toInt()
         if(civInfo.containsBuildingUnique("Gold cost of upgrading military units reduced by 33%"))
             goldCostOfUpgrade = (goldCostOfUpgrade * 0.66f).toInt()
+        if(goldCostOfUpgrade<0) return 0 // For instance, Landsknecht costs less than Spearman, so upgrading would cost negative gold
         return goldCostOfUpgrade
     }