diff --git a/credentials/java/com/google/auth/CredentialTypeForMetrics.java b/credentials/java/com/google/auth/CredentialTypeForMetrics.java
index ccea4ea7b..50c90365c 100644
--- a/credentials/java/com/google/auth/CredentialTypeForMetrics.java
+++ b/credentials/java/com/google/auth/CredentialTypeForMetrics.java
@@ -52,7 +52,7 @@ public enum CredentialTypeForMetrics {
   IMPERSONATED_CREDENTIALS("imp"),
   DO_NOT_SEND("dns");
 
-  private String label;
+  private final String label;
 
   private CredentialTypeForMetrics(String label) {
     this.label = label;
diff --git a/oauth2_http/java/com/google/auth/oauth2/IdTokenProvider.java b/oauth2_http/java/com/google/auth/oauth2/IdTokenProvider.java
index c5b9e9c44..4d9b09e18 100644
--- a/oauth2_http/java/com/google/auth/oauth2/IdTokenProvider.java
+++ b/oauth2_http/java/com/google/auth/oauth2/IdTokenProvider.java
@@ -59,7 +59,7 @@ public enum Option {
     LICENSES_TRUE("licensesTrue"),
     INCLUDE_EMAIL("includeEmail");
 
-    private String option;
+    private final String option;
 
     private Option(String option) {
       this.option = option;
diff --git a/oauth2_http/java/com/google/auth/oauth2/MetricsUtils.java b/oauth2_http/java/com/google/auth/oauth2/MetricsUtils.java
index aa1c712a4..1330457dc 100644
--- a/oauth2_http/java/com/google/auth/oauth2/MetricsUtils.java
+++ b/oauth2_http/java/com/google/auth/oauth2/MetricsUtils.java
@@ -78,7 +78,7 @@ public enum RequestType {
     METADATA_SERVER_PING("mds"),
     UNTRACKED("untracked");
 
-    private String label;
+    private final String label;
 
     private RequestType(String label) {
       this.label = label;