diff --git a/pkl-core/src/main/java/org/pkl/core/runtime/VmExceptionBuilder.java b/pkl-core/src/main/java/org/pkl/core/runtime/VmExceptionBuilder.java
index bb69ccaf6..68ac2fc15 100644
--- a/pkl-core/src/main/java/org/pkl/core/runtime/VmExceptionBuilder.java
+++ b/pkl-core/src/main/java/org/pkl/core/runtime/VmExceptionBuilder.java
@@ -1,5 +1,5 @@
 /*
- * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ * Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -345,6 +345,10 @@ public VmExceptionBuilder withInsertedStackFrames(
     return this;
   }
 
+  public VmExceptionBuilder stackOverflowError() {
+    return evalError("stackOverflow");
+  }
+
   public VmException build() {
     if (message == null) {
       throw new IllegalStateException("No message set.");
diff --git a/pkl-core/src/main/java/org/pkl/core/runtime/VmTyped.java b/pkl-core/src/main/java/org/pkl/core/runtime/VmTyped.java
index da768bb6c..c3160254f 100644
--- a/pkl-core/src/main/java/org/pkl/core/runtime/VmTyped.java
+++ b/pkl-core/src/main/java/org/pkl/core/runtime/VmTyped.java
@@ -204,7 +204,7 @@ public int hashCode() {
 
     for (var key : clazz.getAllRegularPropertyNames()) {
       var value = getCachedValue(key);
-      assert value != null;
+      if (value == null) throw new VmExceptionBuilder().stackOverflowError().build();
       result = 31 * result + value.hashCode();
     }