diff --git a/core/src/main/java/org/teavm/model/MethodDescriptor.java b/core/src/main/java/org/teavm/model/MethodDescriptor.java
index 35d0ae460..5beef6647 100644
--- a/core/src/main/java/org/teavm/model/MethodDescriptor.java
+++ b/core/src/main/java/org/teavm/model/MethodDescriptor.java
@@ -15,12 +15,13 @@
  */
 package org.teavm.model;
 
+import java.io.Serializable;
 import java.util.Arrays;
 
-public class MethodDescriptor {
+public class MethodDescriptor implements Serializable {
     private String name;
     private ValueType[] signature;
-    private int hash;
+    private transient int hash;
 
     public MethodDescriptor(String name, ValueType... signature) {
         if (signature.length < 1) {
diff --git a/core/src/main/java/org/teavm/model/MethodReference.java b/core/src/main/java/org/teavm/model/MethodReference.java
index 6f0ed370c..292f9ef41 100644
--- a/core/src/main/java/org/teavm/model/MethodReference.java
+++ b/core/src/main/java/org/teavm/model/MethodReference.java
@@ -35,8 +35,8 @@ import java.util.stream.Stream;
  */
 public class MethodReference implements Serializable {
     private String className;
-    private transient MethodDescriptor descriptor;
-    private int hash;
+    private MethodDescriptor descriptor;
+    private transient int hash;
 
     public MethodReference(String className, MethodDescriptor descriptor) {
         this.className = className;
diff --git a/core/src/main/java/org/teavm/model/ValueType.java b/core/src/main/java/org/teavm/model/ValueType.java
index 767b24372..e19a6540c 100644
--- a/core/src/main/java/org/teavm/model/ValueType.java
+++ b/core/src/main/java/org/teavm/model/ValueType.java
@@ -27,7 +27,7 @@ public abstract class ValueType implements Serializable {
 
     public static class Object extends ValueType {
         private String className;
-        private int hash;
+        private transient int hash;
 
         public Object(String className) {
             this.className = className;
@@ -126,7 +126,7 @@ public abstract class ValueType implements Serializable {
 
     public static class Array extends ValueType {
         private ValueType itemType;
-        private int hash;
+        private transient int hash;
 
         public Array(ValueType itemType) {
             this.itemType = itemType;
diff --git a/jso/impl/src/main/java/org/teavm/jso/impl/JSClassProcessor.java b/jso/impl/src/main/java/org/teavm/jso/impl/JSClassProcessor.java
index 7bd3a8fab..c111a561b 100644
--- a/jso/impl/src/main/java/org/teavm/jso/impl/JSClassProcessor.java
+++ b/jso/impl/src/main/java/org/teavm/jso/impl/JSClassProcessor.java
@@ -365,7 +365,7 @@ class JSClassProcessor {
         boolean returnByRef = method.getAnnotations().get(JSByRef.class.getName()) != null;
         if (returnByRef && !typeHelper.isSupportedByRefType(method.getResultType())) {
             diagnostics.error(callLocation, "Method {{m0}} is marked with @JSByRef, but does not return valid "
-                    + "array type");
+                    + "array type", method.getReference());
             return false;
         }