diff --git a/com.oracle.truffle.r.nodes.builtin/src/com/oracle/truffle/r/nodes/builtin/helpers/DebugHandling.java b/com.oracle.truffle.r.nodes.builtin/src/com/oracle/truffle/r/nodes/builtin/helpers/DebugHandling.java
index ff6f5b36d84fa8799557ff7c295026fcd2f53472..b18018abf0663f8b5ad7b81e5f1aa4b9b120046a 100644
--- a/com.oracle.truffle.r.nodes.builtin/src/com/oracle/truffle/r/nodes/builtin/helpers/DebugHandling.java
+++ b/com.oracle.truffle.r.nodes.builtin/src/com/oracle/truffle/r/nodes/builtin/helpers/DebugHandling.java
@@ -176,7 +176,9 @@ public class DebugHandling {
                 }
                 accept(element.getSyntaxLHS());
                 for (RSyntaxElement arg : element.getSyntaxArguments()) {
-                    accept(arg);
+                    if (arg != null) {
+                        accept(arg);
+                    }
                 }
                 return null;
             }