diff --git a/core/src/com/unciv/models/ruleset/PolicyBranch.kt b/core/src/com/unciv/models/ruleset/PolicyBranch.kt
index e3127a0e24..92bc6be7a3 100644
--- a/core/src/com/unciv/models/ruleset/PolicyBranch.kt
+++ b/core/src/com/unciv/models/ruleset/PolicyBranch.kt
@@ -3,5 +3,5 @@ package com.unciv.models.ruleset
 class PolicyBranch : Policy() {
     var policies: ArrayList<Policy> = arrayListOf()
     var priorities: HashMap<String, Int> = HashMap()
-    lateinit var era: String
+    var era: String = ""
 }
diff --git a/core/src/com/unciv/models/ruleset/Ruleset.kt b/core/src/com/unciv/models/ruleset/Ruleset.kt
index 1759f79dd4..5ebc80bd65 100644
--- a/core/src/com/unciv/models/ruleset/Ruleset.kt
+++ b/core/src/com/unciv/models/ruleset/Ruleset.kt
@@ -813,6 +813,11 @@ class Ruleset {
             checkUniques(policy, lines, rulesetSpecific, forOptionsPopup)
         }
 
+        for (branch in policyBranches.values)
+            if (branch.era !in eras)
+                lines += "${branch.name} requires era ${branch.era} which does not exist!"
+
+
         for (policy in policyBranches.values.flatMap { it.policies + it })
             if (policy != policies[policy.name])
                 lines += "More than one policy with the name ${policy.name} exists!"