diff --git a/core/src/com/unciv/logic/civilization/diplomacy/CityStateFunctions.kt b/core/src/com/unciv/logic/civilization/diplomacy/CityStateFunctions.kt
index 45d864beec..0ff3c967d0 100644
--- a/core/src/com/unciv/logic/civilization/diplomacy/CityStateFunctions.kt
+++ b/core/src/com/unciv/logic/civilization/diplomacy/CityStateFunctions.kt
@@ -94,7 +94,7 @@ class CityStateFunctions(val civInfo: Civilization) {
                 ?: return null
             if (!receivingCiv.tech.isResearched(uniqueUnit))
                 return null
-            if (uniqueUnit.obsoleteTech != null && receivingCiv.tech.isResearched(uniqueUnit.obsoleteTech!!))
+            if (receivingCiv.tech.isObsolete(uniqueUnit))
                 return null
             return uniqueUnit
         }
diff --git a/core/src/com/unciv/logic/civilization/managers/TechManager.kt b/core/src/com/unciv/logic/civilization/managers/TechManager.kt
index 07c65721ad..ffb5fe0c66 100644
--- a/core/src/com/unciv/logic/civilization/managers/TechManager.kt
+++ b/core/src/com/unciv/logic/civilization/managers/TechManager.kt
@@ -157,6 +157,8 @@ class TechManager : IsPartOfGameInfoSerialization {
 
     fun isResearched(construction: INonPerpetualConstruction): Boolean = construction.requiredTechs().all{ requiredTech -> isResearched(requiredTech) }
 
+    fun isObsolete(unit: BaseUnit): Boolean = unit.techsThatObsoleteThis().any{ obsoleteTech -> isResearched(obsoleteTech) }
+
     fun canBeResearched(techName: String): Boolean {
         val tech = getRuleset().technologies[techName]!!
         if (tech.uniqueObjects.any { it.type == UniqueType.OnlyAvailableWhen && !it.conditionalsApply(civInfo) })