diff --git a/src/main/java/com/twineworks/tweakflow/lang/interpreter/ops/FunctionOp.java b/src/main/java/com/twineworks/tweakflow/lang/interpreter/ops/FunctionOp.java
index cc1fbc66..db655984 100644
--- a/src/main/java/com/twineworks/tweakflow/lang/interpreter/ops/FunctionOp.java
+++ b/src/main/java/com/twineworks/tweakflow/lang/interpreter/ops/FunctionOp.java
@@ -73,7 +73,7 @@ public Value eval(Stack stack, EvaluationContext context) {
         Cell cell = Spaces.resolve(closure, currentStack.getSpace());
 
         // closed over value has not been evaluated yet
-        if (cell.getValue() == null || cell.isDirty()){
+        if (cell.isDirty()){
           closures.put(closure, cell);
           // is currently evaluating
           if (cell.isEvaluating()){