diff --git a/src/main/java/org/apache/commons/math3/optim/BaseOptimizer.java b/src/main/java/org/apache/commons/math3/optim/BaseOptimizer.java
index 12e1dab91..9aff1df26 100644
--- a/src/main/java/org/apache/commons/math3/optim/BaseOptimizer.java
+++ b/src/main/java/org/apache/commons/math3/optim/BaseOptimizer.java
@@ -39,7 +39,7 @@ public abstract class BaseOptimizer<PAIR> {
     /** Iterations counter. */
     protected final Incrementor iterations;
     /** Convergence checker. */
-    private ConvergenceChecker<PAIR> checker;
+    private final ConvergenceChecker<PAIR> checker;
 
     /**
      * @param checker Convergence checker.