diff --git a/src/main/java/arb/expressions/nodes/DerivativeNode.java b/src/main/java/arb/expressions/nodes/DerivativeNode.java
index 527aa2ed0..6c8d56d86 100644
--- a/src/main/java/arb/expressions/nodes/DerivativeNode.java
+++ b/src/main/java/arb/expressions/nodes/DerivativeNode.java
@@ -165,8 +165,7 @@ public <C> Class<? extends C> type()
          Node<E, S, G>
          spliceInto(Expression<E, S, G> newExpression)
   {
-    assert false : "TODO: https://github.com/crowlogic/arb4j/issues/540";
-    return null;
+    return derivative.spliceInto(newExpression);
   }
 
   @Override