diff --git a/com.oracle.truffle.r.runtime/src/com/oracle/truffle/r/runtime/env/REnvironment.java b/com.oracle.truffle.r.runtime/src/com/oracle/truffle/r/runtime/env/REnvironment.java
index 00915a63c5d58c85b0adbe9cbf693ae780de7acb..14ea9d792a67f1d41a999b07344e982b5017d96e 100644
--- a/com.oracle.truffle.r.runtime/src/com/oracle/truffle/r/runtime/env/REnvironment.java
+++ b/com.oracle.truffle.r.runtime/src/com/oracle/truffle/r/runtime/env/REnvironment.java
@@ -111,7 +111,7 @@ public abstract class REnvironment extends RAttributeStorage {
         return implicitClass;
     }
 
-    public static class ContextStateImpl implements RContext.ContextState {
+    public static final class ContextStateImpl implements RContext.ContextState {
         private SearchPath searchPath;
         private final MaterializedFrame globalFrame;
         private Base baseEnv;