diff --git a/src/renderer/renderer.rs b/src/renderer/renderer.rs
index e282791..50f592c 100644
--- a/src/renderer/renderer.rs
+++ b/src/renderer/renderer.rs
@@ -957,24 +957,29 @@ impl<'a> DustRenderer<'a> {
             maybe_ice
                 .as_ref()
                 .map(|ice| ice.get_context_element_reference())
+                .map(|ce| ce.cast_to_type("number"))
         });
         let right_side_ce = right_side.as_ref().map(|maybe_ice| {
             maybe_ice
                 .as_ref()
                 .map(|ice| ice.get_context_element_reference())
+                .map(|ce| ce.cast_to_type("number"))
         });
 
-        // TODO convert string to number or render NaN
-
-        println!(
-            "Doing {:?} {:?} {:?}",
-            left_side, method_rendered, right_side
-        );
+        // println!(
+        //     "Doing {:?} {:?} {:?}",
+        //     left_side, method_rendered, right_side
+        // );
 
         return match method_rendered.as_str() {
             "add" => match (left_side_ce, right_side_ce) {
                 (None, _) | (Some(Err(_)), _) | (_, None) | (_, Some(Err(_))) => None,
-                (Some(Ok(l)), Some(Ok(r))) => l.math_add(r),
+                (Some(Ok(None)), _) | (_, Some(Ok(None))) => Some(IceResult::from_owned(
+                    OwnedLiteral::LString("NaN".to_owned()),
+                )),
+                (Some(Ok(Some(l))), Some(Ok(Some(r)))) => l
+                    .get_context_element_reference()
+                    .math_add(r.get_context_element_reference()),
             },
             "subtract" => todo!(),
             "multiply" => todo!(),