diff --git a/core/src/com/unciv/models/ruleset/Building.kt b/core/src/com/unciv/models/ruleset/Building.kt
index 7def7da5cf..604c1cf909 100644
--- a/core/src/com/unciv/models/ruleset/Building.kt
+++ b/core/src/com/unciv/models/ruleset/Building.kt
@@ -469,7 +469,7 @@ class Building : NamedStats(), IConstruction {
         val improvementUnique = uniqueObjects
                 .firstOrNull { it.placeholderText == "Creates a [] improvement on a specific tile" }
         if (improvementUnique == null) return null
-        return ruleset.tileImprovements[improvementUnique.params[0]]!!
+        return ruleset.tileImprovements[improvementUnique.params[0]]
     }
 
     fun isSellable() = !isWonder && !isNationalWonder && !uniques.contains("Unsellable")
diff --git a/core/src/com/unciv/models/ruleset/Ruleset.kt b/core/src/com/unciv/models/ruleset/Ruleset.kt
index 804c940e1f..ea30d63bb5 100644
--- a/core/src/com/unciv/models/ruleset/Ruleset.kt
+++ b/core/src/com/unciv/models/ruleset/Ruleset.kt
@@ -278,6 +278,9 @@ class Ruleset {
                 lines += "${building.name} requires ${building.requiredBuildingInAllCities} in all cities which does not exist!"
             if (building.providesFreeBuilding != null && !buildings.containsKey(building.providesFreeBuilding!!))
                 lines += "${building.name} provides a free ${building.providesFreeBuilding} which does not exist!"
+            for (unique in building.uniqueObjects)
+                if (unique.placeholderText == "Creates a [] improvement on a specific tile" && !tileImprovements.containsKey(unique.params[0]))
+                    lines += "${building.name} creates a ${unique.params[0]} improvement which does not exist!"
         }
 
         for (resource in tileResources.values) {