diff --git a/java-spiffe-core/src/main/java/spiffe/workloadapi/WorkloadApiClient.java b/java-spiffe-core/src/main/java/spiffe/workloadapi/WorkloadApiClient.java
index 84c38db..f00a71a 100644
--- a/java-spiffe-core/src/main/java/spiffe/workloadapi/WorkloadApiClient.java
+++ b/java-spiffe-core/src/main/java/spiffe/workloadapi/WorkloadApiClient.java
@@ -59,7 +59,7 @@ public class WorkloadApiClient implements Closeable {
     // it is injected in each of the retryHandlers in the watch methods
     private final ScheduledExecutorService retryExecutor;
 
-    private ExecutorService executorService;
+    private final ExecutorService executorService;
 
     private boolean closed;