diff --git a/CedarJava/build.gradle b/CedarJava/build.gradle
index 65de46e7..b4e3afcd 100644
--- a/CedarJava/build.gradle
+++ b/CedarJava/build.gradle
@@ -70,6 +70,7 @@ dependencies {
     implementation 'com.fasterxml.jackson.core:jackson-databind:2.16.1'
     implementation 'com.fasterxml.jackson.datatype:jackson-datatype-jdk8:2.16.1'
     implementation 'org.slf4j:slf4j-api:2.0.12'
+    implementation 'com.google.guava:guava:33.0.0-jre'
     compileOnly 'com.github.spotbugs:spotbugs-annotations:4.8.3'
     testImplementation 'org.slf4j:slf4j-simple:2.0.12'
     testImplementation 'org.junit.jupiter:junit-jupiter-api:5.10.2'
diff --git a/CedarJava/config.sh b/CedarJava/config.sh
index 41cde92b..54ac158c 100755
--- a/CedarJava/config.sh
+++ b/CedarJava/config.sh
@@ -14,7 +14,7 @@ if [ "$(uname)" == "Darwin" ]; then
 else
     ffi_lib_str="    environment 'CEDAR_JAVA_FFI_LIB', '"$parent_dir"/CedarJavaFFI/target/debug/libcedar_java_ffi.so'"
 fi
-sed "85s;.*;$ffi_lib_str;" "build.gradle" > new_build.gradle
+sed "83s;.*;$ffi_lib_str;" "build.gradle" > new_build.gradle
 mv new_build.gradle build.gradle
 
 # In CI, we need to pull the latest cedar-policy to match the latest cedar-integration-tests
@@ -23,7 +23,7 @@ mv new_build.gradle build.gradle
 # If you call this script with `run_int_tests`, we assume you have `cedar` checkout out in the `cedar-java` dir
 if [ "$#" -ne 0 ] && [ "$1" == "run_int_tests" ]; then
     integration_tests_str="    environment 'CEDAR_INTEGRATION_TESTS_ROOT', '"$parent_dir"/cedar/cedar-integration-tests'"
-    sed "84s;.*;$integration_tests_str;" "build.gradle" > new_build.gradle
+    sed "82s;.*;$integration_tests_str;" "build.gradle" > new_build.gradle
     mv new_build.gradle build.gradle
 
     export MUST_RUN_CEDAR_INTEGRATION_TESTS=1
diff --git a/CedarJava/src/main/java/com/cedarpolicy/model/AuthorizationResponse.java b/CedarJava/src/main/java/com/cedarpolicy/model/AuthorizationResponse.java
index ba69a29d..925d2cf3 100644
--- a/CedarJava/src/main/java/com/cedarpolicy/model/AuthorizationResponse.java
+++ b/CedarJava/src/main/java/com/cedarpolicy/model/AuthorizationResponse.java
@@ -19,9 +19,10 @@
 import com.fasterxml.jackson.annotation.JsonCreator;
 import com.fasterxml.jackson.annotation.JsonProperty;
 import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
-import java.util.Collections;
 import java.util.List;
 import java.util.Set;
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableSet;
 
 /**
  * The result of processing an AuthorizationRequest. The answer to the request is contained in the
@@ -53,10 +54,10 @@ public static class Diagnostics {
          * Set of policyID's that caused the decision. For example, when a policy evaluates to Deny,
          * all deny policies that evaluated to True will appear in Reasons.
          */
-        private Set<String> reason;
+        private ImmutableSet<String> reason;
 
         /** Set of errors and warnings returned by Cedar. */
-        private List<String> errors;
+        private ImmutableList<String> errors;
 
         /**
          * Read the reasons and errors from a JSON object.
@@ -68,8 +69,8 @@ public static class Diagnostics {
         public Diagnostics(
                 @JsonProperty("reason") Set<String> reason,
                 @JsonProperty("errors") List<String> errors) {
-            this.errors = Collections.unmodifiableList(errors);
-            this.reason = Collections.unmodifiableSet(reason);
+            this.errors = ImmutableList.copyOf(errors);
+            this.reason = ImmutableSet.copyOf(reason);
         }
 
         /**
diff --git a/CedarJava/src/main/java/com/cedarpolicy/model/slice/TemplateInstantiation.java b/CedarJava/src/main/java/com/cedarpolicy/model/slice/TemplateInstantiation.java
index aa0f4735..ed31afaa 100644
--- a/CedarJava/src/main/java/com/cedarpolicy/model/slice/TemplateInstantiation.java
+++ b/CedarJava/src/main/java/com/cedarpolicy/model/slice/TemplateInstantiation.java
@@ -18,8 +18,8 @@
 
 import com.fasterxml.jackson.annotation.JsonCreator;
 import com.fasterxml.jackson.annotation.JsonProperty;
-import java.util.Collections;
 import java.util.List;
+import com.google.common.collect.ImmutableList;
 
 /** Template instantiation. */
 public class TemplateInstantiation {
@@ -46,7 +46,7 @@ public TemplateInstantiation(
             @JsonProperty("instantiations") List<Instantiation> instantiations) {
         this.templateId = templateId;
         this.resultPolicyId = resultPolicyId;
-        this.instantiations = Collections.unmodifiableList(instantiations);
+        this.instantiations = ImmutableList.copyOf(instantiations);
     }
 
     /** Get the template ID. */