diff --git a/com.oracle.truffle.r.ffi.impl/src/com/oracle/truffle/r/ffi/impl/nodes/CoerceNodes.java b/com.oracle.truffle.r.ffi.impl/src/com/oracle/truffle/r/ffi/impl/nodes/CoerceNodes.java
index bc51d6d45c3eb4590ec0f85ec40df30d74dd49af..b3007b211c50f7552ebd8bfab8cf3bd583b09458 100644
--- a/com.oracle.truffle.r.ffi.impl/src/com/oracle/truffle/r/ffi/impl/nodes/CoerceNodes.java
+++ b/com.oracle.truffle.r.ffi.impl/src/com/oracle/truffle/r/ffi/impl/nodes/CoerceNodes.java
@@ -51,6 +51,7 @@ import com.oracle.truffle.r.runtime.data.RNull;
 import com.oracle.truffle.r.runtime.data.RPairList;
 import com.oracle.truffle.r.runtime.data.RShareable;
 import com.oracle.truffle.r.runtime.data.RStringVector;
+import com.oracle.truffle.r.runtime.data.RSymbol;
 import com.oracle.truffle.r.runtime.data.RTypedValue;
 import com.oracle.truffle.r.runtime.data.model.RAbstractIntVector;
 import com.oracle.truffle.r.runtime.data.model.RAbstractVector;
@@ -75,7 +76,7 @@ public final class CoerceNodes {
             for (int i = 0; i < v.getLength(); i++) {
                 Object element = v.getDataAtAsObject(i);
                 adjustSharing(v, element);
-                RPairList cur = RDataFactory.createPairList(element, RNull.instance, names != null ? names.getDataAt(i) : RNull.instance, gnurType);
+                RPairList cur = RDataFactory.createPairList(element, RNull.instance, names != null ? RDataFactory.createSymbol(names.getDataAt(i)) : RNull.instance, gnurType);
 
                 if (prev == null) {
                     assert head == null;
diff --git a/com.oracle.truffle.r.runtime/src/com/oracle/truffle/r/runtime/data/RArgsValuesAndNames.java b/com.oracle.truffle.r.runtime/src/com/oracle/truffle/r/runtime/data/RArgsValuesAndNames.java
index fee0ee0e9f4f3d1ec84ad3b192ca03f0bdf94f8d..f0182160856b72173b12e5dd533ec35f7ad2f186 100644
--- a/com.oracle.truffle.r.runtime/src/com/oracle/truffle/r/runtime/data/RArgsValuesAndNames.java
+++ b/com.oracle.truffle.r.runtime/src/com/oracle/truffle/r/runtime/data/RArgsValuesAndNames.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013, 2017, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2013, 2018, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -108,7 +108,7 @@ public final class RArgsValuesAndNames extends RObject implements RTypedValue {
         assert signature.getLength() == getLength();
         for (int i = 0; i < getLength(); i++) {
             String name = signature.getName(i);
-            RPairList cur = RDataFactory.createPairList(getArgument(i), RNull.instance, name != null ? name : RNull.instance, SEXPTYPE.DOTSXP);
+            RPairList cur = RDataFactory.createPairList(getArgument(i), RNull.instance, name != null ? RDataFactory.createSymbol(name) : RNull.instance, SEXPTYPE.DOTSXP);
 
             if (head == null) {
                 head = cur;
diff --git a/com.oracle.truffle.r.runtime/src/com/oracle/truffle/r/runtime/data/RPairList.java b/com.oracle.truffle.r.runtime/src/com/oracle/truffle/r/runtime/data/RPairList.java
index 8ba6f70a6a9a78a99fd0fcf5609becef434cf1af..b729095f5df82ea0face701e2c98ccf540b0eb45 100644
--- a/com.oracle.truffle.r.runtime/src/com/oracle/truffle/r/runtime/data/RPairList.java
+++ b/com.oracle.truffle.r.runtime/src/com/oracle/truffle/r/runtime/data/RPairList.java
@@ -45,7 +45,13 @@ import com.oracle.truffle.r.runtime.gnur.SEXPTYPE;
  * {@code null} is never allowed as a value for the tag, car or cdr, only the type.
  */
 public final class RPairList extends RSharingAttributeStorage implements RAbstractContainer, Iterable<RPairList> {
+    /**
+     * Data of the current pair list cell.
+     */
     private Object car = RNull.instance;
+    /**
+     * Link to the next {@link RPairList} cell or {@link RNull} if last.
+     */
     private Object cdr = RNull.instance;
     /**
      * Externally, i.e., when serialized, this is either a SYMSXP ({@link RSymbol}) or an
@@ -336,9 +342,7 @@ public final class RPairList extends RSharingAttributeStorage implements RAbstra
         int i = 0;
         while (true) {
             data[i] = Utils.toString(pl.tag);
-            if (pl.tag == RRuntime.STRING_NA) {
-                complete = false;
-            }
+            complete &= data[i] != RRuntime.STRING_NA;
             if (isNull(pl.cdr)) {
                 break;
             }
@@ -353,7 +357,7 @@ public final class RPairList extends RSharingAttributeStorage implements RAbstra
         Object p = this;
         for (int i = 0; i < newNames.getLength() && !isNull(p); i++) {
             RPairList pList = (RPairList) p;
-            pList.tag = newNames.getDataAt(i);
+            pList.tag = RDataFactory.createSymbol(newNames.getDataAt(i));
             p = pList.cdr;
         }
     }