diff --git a/com.oracle.truffle.r.nodes/src/com/oracle/truffle/r/nodes/attributes/SpecialAttributesFunctions.java b/com.oracle.truffle.r.nodes/src/com/oracle/truffle/r/nodes/attributes/SpecialAttributesFunctions.java
index 53b01a29ef993a1542c262681918da2c6dcfdf6b..77cb4bb1ea1f8c668f5ecac08ac2b68d7e22d7cc 100644
--- a/com.oracle.truffle.r.nodes/src/com/oracle/truffle/r/nodes/attributes/SpecialAttributesFunctions.java
+++ b/com.oracle.truffle.r.nodes/src/com/oracle/truffle/r/nodes/attributes/SpecialAttributesFunctions.java
@@ -838,7 +838,8 @@ public final class SpecialAttributesFunctions {
         }
 
         public final RList getDimNames(Object x) {
-            return (RList) execute(x);
+            Object result = execute(x);
+            return result == RNull.instance ? null : (RList) result;
         }
 
         @Specialization(insertBefore = "getAttrFromAttributable")