diff --git a/com.oracle.truffle.r.ffi.impl/src/com/oracle/truffle/r/ffi/impl/nodes/AttributesAccessNodes.java b/com.oracle.truffle.r.ffi.impl/src/com/oracle/truffle/r/ffi/impl/nodes/AttributesAccessNodes.java
index 1ce91a921d39bd1c33dc932b7a4d26dfccfb24e5..7bcfe69ff77bebcebcfb819fb3f025d3c09c43a5 100644
--- a/com.oracle.truffle.r.ffi.impl/src/com/oracle/truffle/r/ffi/impl/nodes/AttributesAccessNodes.java
+++ b/com.oracle.truffle.r.ffi.impl/src/com/oracle/truffle/r/ffi/impl/nodes/AttributesAccessNodes.java
@@ -124,13 +124,13 @@ public final class AttributesAccessNodes {
         @Child protected CopyOfRegAttributesNode copyRegAttributes;
 
         @Specialization
-        public Object doList(RAttributeStorage x, RAttributeStorage y) {
+        public int doRAttributeStorage(RAttributeStorage x, RAttributeStorage y) {
             if (copyRegAttributes == null) {
                 CompilerDirectives.transferToInterpreterAndInvalidate();
                 copyRegAttributes = CopyOfRegAttributesNode.create();
             }
             copyRegAttributes.execute(x, y);
-            return RNull.instance;
+            return 0;
         }
 
         @Fallback
diff --git a/com.oracle.truffle.r.ffi.impl/src/com/oracle/truffle/r/ffi/impl/nodes/EnvNodes.java b/com.oracle.truffle.r.ffi.impl/src/com/oracle/truffle/r/ffi/impl/nodes/EnvNodes.java
index 57441100e9446d379cead2d499ae288a22858a4c..4dc716fc421f8bcf8bd2be5503c3dfb23a69616b 100644
--- a/com.oracle.truffle.r.ffi.impl/src/com/oracle/truffle/r/ffi/impl/nodes/EnvNodes.java
+++ b/com.oracle.truffle.r.ffi.impl/src/com/oracle/truffle/r/ffi/impl/nodes/EnvNodes.java
@@ -27,7 +27,6 @@ import com.oracle.truffle.api.dsl.Specialization;
 import com.oracle.truffle.api.dsl.TypeSystemReference;
 import static com.oracle.truffle.r.ffi.impl.common.RFFIUtils.guaranteeInstanceOf;
 import com.oracle.truffle.r.runtime.RInternalError;
-import com.oracle.truffle.r.runtime.data.RNull;
 import com.oracle.truffle.r.runtime.data.RSymbol;
 import com.oracle.truffle.r.runtime.data.RTypes;
 import com.oracle.truffle.r.runtime.env.REnvironment;
@@ -38,14 +37,14 @@ public class EnvNodes {
     public abstract static class LockBindingNode extends FFIUpCallNode.Arg2 {
 
         @Specialization
-        Object lock(RSymbol sym, REnvironment env) {
+        int lock(RSymbol sym, REnvironment env) {
             // TODO copied from EnvFunctions.LockBinding
             env.lockBinding(sym.getName());
-            return RNull.instance;
+            return 0;
         }
 
         @Fallback
-        Object lock(Object sym, Object env) {
+        int lock(Object sym, Object env) {
             guaranteeInstanceOf(sym, RSymbol.class);
             guaranteeInstanceOf(env, REnvironment.class);
             throw RInternalError.shouldNotReachHere();
@@ -60,14 +59,14 @@ public class EnvNodes {
     public abstract static class UnlockBindingNode extends FFIUpCallNode.Arg2 {
 
         @Specialization
-        Object unlock(RSymbol sym, REnvironment env) {
+        int unlock(RSymbol sym, REnvironment env) {
             // TODO copied from EnvFunctions.LockBinding
             env.unlockBinding(sym.getName());
-            return RNull.instance;
+            return 0;
         }
 
         @Fallback
-        Object unlock(Object sym, Object env) {
+        int unlock(Object sym, Object env) {
             guaranteeInstanceOf(sym, RSymbol.class);
             guaranteeInstanceOf(env, REnvironment.class);
             throw RInternalError.shouldNotReachHere();