diff --git a/core/src/com/unciv/models/ruleset/Building.kt b/core/src/com/unciv/models/ruleset/Building.kt
index 71e797ab42..430dce06dd 100644
--- a/core/src/com/unciv/models/ruleset/Building.kt
+++ b/core/src/com/unciv/models/ruleset/Building.kt
@@ -307,6 +307,8 @@ class Building : NamedStats(), IConstruction {
         if (isNationalWonder) {
             if (civInfo.cities.any { it.cityConstructions.isBuilt(name) })
                 return "National Wonder is already built"
+            if (requiredBuildingInAllCities != null && civInfo.gameInfo.ruleSet.buildings[requiredBuildingInAllCities!!] == null)
+                return "Required building in all cities does not exist in the ruleset!"
             if (requiredBuildingInAllCities != null
                     && civInfo.cities.any {
                         !it.isPuppet && !it.cityConstructions
diff --git a/core/src/com/unciv/models/ruleset/Ruleset.kt b/core/src/com/unciv/models/ruleset/Ruleset.kt
index 075412909b..a5a385bd57 100644
--- a/core/src/com/unciv/models/ruleset/Ruleset.kt
+++ b/core/src/com/unciv/models/ruleset/Ruleset.kt
@@ -273,6 +273,8 @@ class Ruleset {
                 lines += "${building.name} replaces ${building.replaces} which does not exist!"
             if (building.requiredBuilding != null && !buildings.containsKey(building.requiredBuilding!!))
                 lines += "${building.name} requires ${building.requiredBuilding} which does not exist!"
+            if (building.requiredBuildingInAllCities != null && !buildings.containsKey(building.requiredBuildingInAllCities!!))
+                lines += "${building.name} requires ${building.requiredBuildingInAllCities} in all cities which does not exist!"
         }
 
         for (resource in tileResources.values) {