diff --git a/src/objects/js-locale.cc b/src/objects/js-locale.cc
index 64644abad2..e3fee128f8 100644
--- a/src/objects/js-locale.cc
+++ b/src/objects/js-locale.cc
@@ -177,19 +177,24 @@ int32_t weekdayFromEDaysOfWeek(icu::Calendar::EDaysOfWeek eDaysOfWeek) {
 
 }  // namespace
 
-bool JSLocale::Is38AlphaNumList(const std::string& value) {
-  std::size_t found_dash = value.find("-");
-  std::size_t found_underscore = value.find("_");
-  if (found_dash == std::string::npos &&
-      found_underscore == std::string::npos) {
-    return IsAlphanum(value, 3, 8);
+bool JSLocale::Is38AlphaNumList(const std::string& in) {
+  std::string value = in;
+  while (true) {
+    std::size_t found_dash = value.find("-");
+    std::size_t found_underscore = value.find("_");
+    if (found_dash == std::string::npos &&
+        found_underscore == std::string::npos) {
+      return IsAlphanum(value, 3, 8);
+    }
+    if (found_underscore == std::string::npos ||
+        found_dash < found_underscore) {
+      if (!IsAlphanum(value.substr(0, found_dash), 3, 8)) return false;
+      value = value.substr(found_dash + 1);
+    } else {
+      if (!IsAlphanum(value.substr(0, found_underscore), 3, 8)) return false;
+      value = value.substr(found_underscore + 1);
+    }
   }
-  if (found_underscore == std::string::npos || found_dash < found_underscore) {
-    return IsAlphanum(value.substr(0, found_dash), 3, 8) &&
-           JSLocale::Is38AlphaNumList(value.substr(found_dash + 1));
-  }
-  return IsAlphanum(value.substr(0, found_underscore), 3, 8) &&
-         JSLocale::Is38AlphaNumList(value.substr(found_underscore + 1));
 }
 
 bool JSLocale::Is3Alpha(const std::string& value) {
diff --git a/test/intl/intl.status b/test/intl/intl.status
index 8c223580db..01847d6d02 100644
--- a/test/intl/intl.status
+++ b/test/intl/intl.status
@@ -31,6 +31,11 @@
   'overrides/caching': [PASS, FAIL],
 }],  # ALWAYS
 
+['asan == True or msan == True or tsan == True', {
+  # Take too long to run
+  'regress-12059': [SKIP],
+}],
+
 ['gc_stress', {
   # Push limit of stack, too flaky with machine with more memory.
   'regress-1130489': [SKIP],
diff --git a/test/intl/regress-12059.js b/test/intl/regress-12059.js
new file mode 100644
index 0000000000..dfe02e2687
--- /dev/null
+++ b/test/intl/regress-12059.js
@@ -0,0 +1,18 @@
+// Copyright 2021 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+assertThrows(
+    () => new Intl.DateTimeFormat('en', {calendar: 'abc-'.repeat(100000)}),
+    RangeError,
+    "Invalid calendar : " + ('abc-'.repeat(100000)));
+
+assertThrows(
+    () => new Intl.DateTimeFormat('en', {calendar: 'abc_'.repeat(100000)}),
+    RangeError,
+    "Invalid calendar : " + ('abc_'.repeat(100000)));
+
+assertThrows(
+    () => new Intl.DateTimeFormat('en', {calendar: 'abc_efgh-'.repeat(100000)}),
+    RangeError,
+    "Invalid calendar : " + ('abc_efgh-'.repeat(100000)));