diff --git a/src/untimed_monitoring_combinators.rs b/src/untimed_monitoring_combinators.rs
index aaa4a2a..d95cacb 100644
--- a/src/untimed_monitoring_combinators.rs
+++ b/src/untimed_monitoring_combinators.rs
@@ -275,41 +275,42 @@ pub fn var(ctx: &dyn StreamContext<Value>, x: VarName) -> OutputStream<Value> {
 // Defer for an UntimedLolaExpression using the lola_expression parser
 pub fn defer(
     ctx: &dyn StreamContext<Value>,
-    prop_stream: OutputStream<Value>,
+    mut prop_stream: OutputStream<Value>,
     history_length: usize,
 ) -> OutputStream<Value> {
     /* Subcontext with current values only*/
     let subcontext = ctx.subcontext(history_length);
-    /*unfold() creates a Stream from a seed value.*/
-    Box::pin(stream::unfold(
-        (subcontext, prop_stream, None::<Value>),
-        |(subcontext, mut x, saved)| async move {
-            /* x.next() returns None if we are done unfolding. Return in that case.*/
-            let current = x.next().await?;
-            /* If we have a saved state then use that otherwise use current */
-            let defer_str = saved.unwrap_or_else(|| current);
-
-            match defer_str {
+
+    Box::pin(stream! {
+        let mut eval_output_stream: Option<OutputStream<Value>> = None;
+
+        // Yield Unknown until we have a value to evaluate, then evaluate it
+        while let Some(current) = prop_stream.next().await {
+            match current {
                 Value::Str(defer_s) => {
+                    // We have a string to evaluate so do so
                     let defer_parse = &mut defer_s.as_str();
-                    let expr = match lola_expression.parse_next(defer_parse) {
-                        Ok(expr) => expr,
-                        Err(_) => unimplemented!("Invalid eval str"),
-                    };
-                    let mut es = UntimedLolaSemantics::to_async_stream(expr, subcontext.deref());
-                    let eval_res = es.next().await?;
-                    subcontext.advance();
-                    return Some((eval_res, (subcontext, x, Some(Value::Str(defer_s)))));
+                    let expr = lola_expression.parse_next(defer_parse)
+                        .expect("Invalid eval str");
+                    eval_output_stream = Some(UntimedLolaSemantics::to_async_stream(expr, subcontext.deref()));
+                    break;
                 }
                 Value::Unknown => {
                     // Consume a sample from the subcontext but return Unknown (aka. Waiting)
                     subcontext.advance();
-                    Some((Value::Unknown, (subcontext, x, None)))
+                    yield Value::Unknown;
                 }
-                _ => panic!("We did not have memory and defer_str was not a Str"),
+                _ => panic!("Invalid defer property type {:?}", current)
             }
-        },
-    ))
+        }
+        let mut eval_output_stream = eval_output_stream.expect("No eval stream");
+
+        // Yield the saved value until the inner stream is done
+        while let Some(eval_res) = eval_output_stream.next().await {
+            subcontext.advance();
+            yield eval_res;
+        }
+    })
 }
 
 // Update for a synchronized language - in this case UntimedLolaSemantics.