diff --git a/com.oracle.truffle.r.nodes.builtin/src/com/oracle/truffle/r/nodes/builtin/base/BasePackage.java b/com.oracle.truffle.r.nodes.builtin/src/com/oracle/truffle/r/nodes/builtin/base/BasePackage.java
index 0650d59a1b7c4b3542b0aa58d5ce8fb5284d106e..a1eb0d12b6a2843765e0b8f1a2cab101114a6e74 100644
--- a/com.oracle.truffle.r.nodes.builtin/src/com/oracle/truffle/r/nodes/builtin/base/BasePackage.java
+++ b/com.oracle.truffle.r.nodes.builtin/src/com/oracle/truffle/r/nodes/builtin/base/BasePackage.java
@@ -167,6 +167,7 @@ public class BasePackage extends RBuiltinPackage {
         add(CumMin.class, CumMinNodeGen::create);
         add(CumProd.class, CumProdNodeGen::create);
         add(CumSum.class, CumSumNodeGen::create);
+        add(CacheClass.class, CacheClassNodeGen::create);
         add(Date.class, DateNodeGen::create);
         add(DatePOSIXFunctions.Date2POSIXlt.class, DatePOSIXFunctionsFactory.Date2POSIXltNodeGen::create);
         add(DatePOSIXFunctions.AsPOSIXct.class, DatePOSIXFunctionsFactory.AsPOSIXctNodeGen::create);
diff --git a/com.oracle.truffle.r.nodes.builtin/src/com/oracle/truffle/r/nodes/builtin/base/CacheClass.java b/com.oracle.truffle.r.nodes.builtin/src/com/oracle/truffle/r/nodes/builtin/base/CacheClass.java
new file mode 100644
index 0000000000000000000000000000000000000000..41e02a380d3aabee9cf18e4c9c4e6f1db5e7fcb9
--- /dev/null
+++ b/com.oracle.truffle.r.nodes.builtin/src/com/oracle/truffle/r/nodes/builtin/base/CacheClass.java
@@ -0,0 +1,43 @@
+/*
+ * This material is distributed under the GNU General Public License
+ * Version 2. You may review the terms of this license at
+ * http://www.gnu.org/licenses/gpl-2.0.html
+ *
+ * Copyright (c) 1995, 1996, 1997  Robert Gentleman and Ross Ihaka
+ * Copyright (c) 1995-2014, The R Core Team
+ * Copyright (c) 2002-2008, The R Foundation
+ * Copyright (c) 2015, Oracle and/or its affiliates
+ *
+ * All rights reserved.
+ */
+package com.oracle.truffle.r.nodes.builtin.base;
+
+import static com.oracle.truffle.r.runtime.RBuiltinKind.*;
+
+import com.oracle.truffle.api.CompilerDirectives.TruffleBoundary;
+import com.oracle.truffle.api.dsl.*;
+import com.oracle.truffle.r.nodes.builtin.*;
+import com.oracle.truffle.r.runtime.*;
+import com.oracle.truffle.r.runtime.context.RContext;
+import com.oracle.truffle.r.runtime.data.RStringVector;
+import com.oracle.truffle.r.runtime.data.model.*;
+
+@RBuiltin(name = ".cache_class", kind = PRIMITIVE, parameterNames = {"class", "extends"})
+public abstract class CacheClass extends RBuiltinNode {
+
+    @TruffleBoundary
+    @Specialization
+    protected RAbstractStringVector getClass(Object cl, RAbstractStringVector ext) {
+        controlVisibility();
+        String clString;
+        if (cl instanceof String) {
+            clString = (String) cl;
+        } else if (cl instanceof RStringVector && ((RStringVector) cl).getLength() == 1) {
+            clString = ((RStringVector) cl).getDataAt(0);
+        } else {
+            throw RError.error(this, RError.Message.GENERIC, "invalid class argument to internal .class_cache");
+        }
+        RContext.getInstance().putS4Extends(clString, ext.materialize());
+        return null;
+    }
+}
diff --git a/com.oracle.truffle.r.nodes/src/com/oracle/truffle/r/nodes/function/ClassHierarchyNode.java b/com.oracle.truffle.r.nodes/src/com/oracle/truffle/r/nodes/function/ClassHierarchyNode.java
index e5c7e1e14daa7b91a8518ccf9b50e6871991cbec..ef8473cef0a66b31f64dd250098b8778e2c49b9d 100644
--- a/com.oracle.truffle.r.nodes/src/com/oracle/truffle/r/nodes/function/ClassHierarchyNode.java
+++ b/com.oracle.truffle.r.nodes/src/com/oracle/truffle/r/nodes/function/ClassHierarchyNode.java
@@ -155,6 +155,7 @@ abstract class S4Class extends RBaseNode {
             // the assumption here is that R function can only return either a String or
             // RStringVector
             s4Extends = (RStringVector) castToVector.execute(RContext.getEngine().evalFunction(sExtendsForS3Function, methodsEnv.getFrame(), classAttr));
+            RContext.getInstance().putS4Extends(classAttr, s4Extends);
         }
         return s4Extends;
     }
diff --git a/mx.fastr/copyrights/overrides b/mx.fastr/copyrights/overrides
index 33e55dbe359fd1a3d42d008e875e2f9c91def8d1..bbadf0434a3330a16ddc71327afd3683b1951965 100644
--- a/mx.fastr/copyrights/overrides
+++ b/mx.fastr/copyrights/overrides
@@ -99,6 +99,7 @@ com.oracle.truffle.r.nodes.builtin/src/com/oracle/truffle/r/nodes/builtin/base/B
 com.oracle.truffle.r.nodes.builtin/src/com/oracle/truffle/r/nodes/builtin/base/BaseVariables.java,gnu_r.copyright
 com.oracle.truffle.r.nodes.builtin/src/com/oracle/truffle/r/nodes/builtin/base/Bincode.java,gnu_r.copyright
 com.oracle.truffle.r.nodes.builtin/src/com/oracle/truffle/r/nodes/builtin/base/BitwiseFunctions.java,purdue.copyright
+com.oracle.truffle.r.nodes.builtin/src/com/oracle/truffle/r/nodes/builtin/base/CacheClass.java,gnu_r_gentleman_ihaka.copyright
 com.oracle.truffle.r.nodes.builtin/src/com/oracle/truffle/r/nodes/builtin/base/CharMatch.java,purdue.copyright
 com.oracle.truffle.r.nodes.builtin/src/com/oracle/truffle/r/nodes/builtin/base/ColMeans.java,purdue.copyright
 com.oracle.truffle.r.nodes.builtin/src/com/oracle/truffle/r/nodes/builtin/base/ConditionFunctions.java,gnu_r.copyright