diff --git a/jdk/make/src/classes/build/tools/tzdb/TzdbZoneRulesCompiler.java b/jdk/make/src/classes/build/tools/tzdb/TzdbZoneRulesCompiler.java
index 9f1204ca7fe..28c951e8dfa 100644
--- a/jdk/make/src/classes/build/tools/tzdb/TzdbZoneRulesCompiler.java
+++ b/jdk/make/src/classes/build/tools/tzdb/TzdbZoneRulesCompiler.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2012, 2024, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -248,7 +248,7 @@ private void outputFile(Path dstFile, String version,
             // link version-region-rules
             out.writeShort(builtZones.size());
             for (Map.Entry<String, ZoneRules> entry : builtZones.entrySet()) {
-                 int regionIndex = Arrays.binarySearch(regionArray, entry.getKey());
+                 int regionIndex = findRegionIndex(regionArray, entry.getKey());
                  int rulesIndex = rulesList.indexOf(entry.getValue());
                  out.writeShort(regionIndex);
                  out.writeShort(rulesIndex);
@@ -256,8 +256,8 @@ private void outputFile(Path dstFile, String version,
             // alias-region
             out.writeShort(links.size());
             for (Map.Entry<String, String> entry : links.entrySet()) {
-                 int aliasIndex = Arrays.binarySearch(regionArray, entry.getKey());
-                 int regionIndex = Arrays.binarySearch(regionArray, entry.getValue());
+                 int aliasIndex = findRegionIndex(regionArray, entry.getKey());
+                 int regionIndex = findRegionIndex(regionArray, entry.getValue());
                  out.writeShort(aliasIndex);
                  out.writeShort(regionIndex);
             }
@@ -286,6 +286,14 @@ private void outputFile(Path dstFile, String version,
     /** The built zones. */
     private final SortedMap<String, ZoneRules> builtZones = new TreeMap<>();
 
+    private static int findRegionIndex(String[] regionArray, String region) {
+        int index = Arrays.binarySearch(regionArray, region);
+        if (index < 0) {
+            throw new IllegalArgumentException("Unknown region: " + region);
+        }
+        return index;
+    }
+
     /** Whether to output verbose messages. */
     private boolean verbose;