diff --git a/src/Engine/ProtoCore/Lang/CallSite.cs b/src/Engine/ProtoCore/Lang/CallSite.cs
index d3e59eb2ba2..1385de522e8 100644
--- a/src/Engine/ProtoCore/Lang/CallSite.cs
+++ b/src/Engine/ProtoCore/Lang/CallSite.cs
@@ -1771,7 +1771,7 @@ private StackValue ExecWithRISlowPath(
                 StackValue[] retSVs = new StackValue[retSize];
 
                 SingleRunTraceData retTrace = newTraceData;
-                retTrace.NestedData = new List<SingleRunTraceData>(); //this will shadow the SVs as they are created
+                retTrace.NestedData = new List<SingleRunTraceData>(retSize); //this will shadow the SVs as they are created
 
                 //Populate out the size of the list with default values
                 //@TODO:Luke perf optimisation here