diff --git a/jvm/CHANGELOG.md b/jvm/CHANGELOG.md
index 8a102a7e..41b8075e 100644
--- a/jvm/CHANGELOG.md
+++ b/jvm/CHANGELOG.md
@@ -14,6 +14,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 - Off-by-one in the error message for a VCR key mismatch. ([#526](https://github.com/diffplug/selfie/pull/526))
 - Fix `StringIndexOutOfBoundsException` when an empty snapshot had a facet added. (fixes [#529](https://github.com/diffplug/selfie/issues/529))
+- Fix `ClassCastException` when multiple nested test cases need to update snapshot. (fixes [#531](https://github.com/diffplug/selfie/issues/531))
 
 ## [2.5.1] - 2025-03-04
 ### Fixed
diff --git a/jvm/selfie-lib/src/commonMain/kotlin/com/diffplug/selfie/ArrayMap.kt b/jvm/selfie-lib/src/commonMain/kotlin/com/diffplug/selfie/ArrayMap.kt
index e5699a32..cc1afcb0 100644
--- a/jvm/selfie-lib/src/commonMain/kotlin/com/diffplug/selfie/ArrayMap.kt
+++ b/jvm/selfie-lib/src/commonMain/kotlin/com/diffplug/selfie/ArrayMap.kt
@@ -287,10 +287,12 @@ class ArraySet<K : Comparable<K>>(private val data: Array<Any>) : ListBackedSet<
       else -> {
         // TODO: use idxInsert and arrayCopy to do this faster, see ArrayMap#insert
         val array = Array(size + 1) { if (it < size) data[it] else key }
+
         if (key is String) {
           array.sortWith(STRING_SLASHFIRST as Comparator<Any>)
         } else {
-          (array as Array<K>).sort()
+          array.sortWith(
+              Comparator { a, b -> @Suppress("UNCHECKED_CAST") (a as K).compareTo(b as K) })
         }
         ArraySet(array)
       }
diff --git a/jvm/selfie-lib/src/commonTest/kotlin/com/diffplug/selfie/ArrayMapTest.kt b/jvm/selfie-lib/src/commonTest/kotlin/com/diffplug/selfie/ArrayMapTest.kt
index f72025b7..bb259cf9 100644
--- a/jvm/selfie-lib/src/commonTest/kotlin/com/diffplug/selfie/ArrayMapTest.kt
+++ b/jvm/selfie-lib/src/commonTest/kotlin/com/diffplug/selfie/ArrayMapTest.kt
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2023-2024 DiffPlug
+ * Copyright (C) 2023-2025 DiffPlug
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -173,3 +173,40 @@ class ArrayMapTest {
     map.minusSortedIndices(listOf(0, 2, 3, 6, 7, 8)).toString() shouldBe "{1=1, 4=4, 5=5}"
   }
 }
+
+class ArraySetTest() {
+  @Test
+  fun empty() {
+    val empty = ArraySet.empty<String>()
+    assertEmpty(empty)
+  }
+
+  @Test
+  fun addition() {
+    var mySet = ArraySet.empty<String>()
+    assertEmpty(mySet)
+
+    mySet = mySet.plusOrThis("one")
+    assertSingle(mySet, "one")
+    mySet = mySet.plusOrThis("one")
+    assertSingle(mySet, "one")
+    mySet = mySet.plusOrThis("two")
+    assertDouble(mySet, "one", "two")
+  }
+  private fun assertEmpty(map: ArraySet<String>) {
+    map.size shouldBe 0
+  }
+  private fun assertSingle(map: ArraySet<String>, key: String) {
+    map.size shouldBe 1
+    map.contains(key) shouldBe true
+  }
+  private fun assertDouble(
+      map: ArraySet<String>,
+      key1: String,
+      key2: String,
+  ) {
+    map.size shouldBe 2
+    map.contains(key1) shouldBe true
+    map.contains(key2) shouldBe true
+  }
+}