diff --git a/compiler/mono/src/decision_tree.rs b/compiler/mono/src/decision_tree.rs
index 7e9395e781..04d25e0b78 100644
--- a/compiler/mono/src/decision_tree.rs
+++ b/compiler/mono/src/decision_tree.rs
@@ -1036,8 +1036,8 @@ fn path_to_expr_help<'a>(
     let mut it = instructions.iter().peekable();
 
     while let Some(PathInstruction { index, tag_id }) = it.next() {
-        match Wrapped::opt_from_layout(&layout) {
-            None => {
+        match Wrapped::is_indexable(&layout) {
+            false => {
                 // this MUST be an index into a single-element (hence unwrapped) record
 
                 debug_assert_eq!(*index, 0, "{:?}", &layout);
@@ -1063,7 +1063,7 @@ fn path_to_expr_help<'a>(
 
                 break;
             }
-            Some(wrapped) => {
+            true => {
                 let index = *index;
 
                 let (inner_layout, inner_expr) = match layout {
@@ -1078,6 +1078,7 @@ fn path_to_expr_help<'a>(
                         (union_layout.layout_at(*tag_id as u8, index as usize), expr)
                     }
                     Layout::Struct(field_layouts) => {
+                        let wrapped = Wrapped::opt_from_layout(&layout).unwrap();
                         debug_assert!(field_layouts.len() > 1);
                         debug_assert_eq!(wrapped, Wrapped::RecordOrSingleTagUnion);
 
diff --git a/compiler/mono/src/ir.rs b/compiler/mono/src/ir.rs
index 5652fe3212..d840663142 100644
--- a/compiler/mono/src/ir.rs
+++ b/compiler/mono/src/ir.rs
@@ -1032,6 +1032,17 @@ impl Wrapped {
         }
     }
 
+    pub fn is_indexable(layout: &Layout<'_>) -> bool {
+        match layout {
+            Layout::Struct(fields) => match fields.len() {
+                _ => true,
+            },
+
+            Layout::Union(variant) => true,
+            _ => false,
+        }
+    }
+
     pub fn opt_from_layout(layout: &Layout<'_>) -> Option<Self> {
         match layout {
             Layout::Struct(fields) => match fields.len() {
@@ -1056,6 +1067,7 @@ impl Wrapped {
                     NonNullableUnwrapped(_) => Some(Wrapped::LikeARoseTree),
 
                     NullableWrapped { .. } | NullableUnwrapped { .. } => {
+                        todo!();
                         Some(Wrapped::MultiTagUnion)
                     }
                 }
@@ -2133,6 +2145,8 @@ fn specialize_external<'a>(
                     match closure_layout.layout_for_member(proc_name) {
                         ClosureRepresentation::Union {
                             tag_layout: field_layouts,
+                            union_layout,
+                            tag_id,
                             ..
                         } => {
                             debug_assert_eq!(field_layouts.len() - 1, captured.len());
@@ -2143,11 +2157,11 @@ fn specialize_external<'a>(
                                 index += 1;
 
                                 // TODO therefore should the wrapped here not be RecordOrSingleTagUnion?
-                                let expr = Expr::AccessAtIndex {
-                                    index: index as _,
-                                    field_layouts,
+                                let expr = Expr::CoerceToTagId {
+                                    tag_id,
                                     structure: Symbol::ARG_CLOSURE,
-                                    wrapped,
+                                    index: index as _,
+                                    union_layout,
                                 };
 
                                 let layout = field_layouts[index];
@@ -4074,21 +4088,17 @@ fn construct_closure_data<'a>(
             tag_layout: _,
             union_size,
             tag_name,
+            union_layout,
         } => {
             let tag_id_symbol = env.unique_symbol();
             let mut tag_symbols = Vec::with_capacity_in(symbols.len() + 1, env.arena);
             tag_symbols.push(tag_id_symbol);
             tag_symbols.extend(symbols);
 
-            let tag_layout = match lambda_set.runtime_representation() {
-                Layout::Union(inner) => inner,
-                _ => unreachable!(),
-            };
-
             let expr1 = Expr::Literal(Literal::Int(tag_id as i128));
             let expr2 = Expr::Tag {
                 tag_id,
-                tag_layout,
+                tag_layout: union_layout,
                 union_size,
                 tag_name,
                 arguments: tag_symbols.into_bump_slice(),
diff --git a/compiler/mono/src/layout.rs b/compiler/mono/src/layout.rs
index 7fdb9754d6..05e02cf9ca 100644
--- a/compiler/mono/src/layout.rs
+++ b/compiler/mono/src/layout.rs
@@ -200,6 +200,7 @@ pub enum ClosureRepresentation<'a> {
         tag_name: TagName,
         tag_id: u8,
         union_size: u8,
+        union_layout: UnionLayout<'a>,
     },
     /// the representation is anything but a union
     Other(Layout<'a>),
@@ -241,6 +242,7 @@ impl<'a> LambdaSet<'a> {
                             tag_id: index as u8,
                             tag_layout: tags[index],
                             tag_name: TagName::Closure(function_symbol),
+                            union_layout: *union,
                         }
                     }
                     UnionLayout::Recursive(_) => todo!("recursive closures"),
diff --git a/compiler/test_mono/generated/specialize_closures.txt b/compiler/test_mono/generated/specialize_closures.txt
index b67e0561b7..5534042fa3 100644
--- a/compiler/test_mono/generated/specialize_closures.txt
+++ b/compiler/test_mono/generated/specialize_closures.txt
@@ -22,13 +22,13 @@ procedure Test.1 (Test.2, Test.3):
     
 
 procedure Test.7 (Test.10, #Attr.12):
-    let Test.4 = Index 1 #Attr.12;
+    let Test.4 = CoerceToTagId (Id 0) (Index 1) #Attr.12;
     let Test.29 = CallByName Num.24 Test.10 Test.4;
     ret Test.29;
 
 procedure Test.8 (Test.11, #Attr.12):
-    let Test.6 = Index 2 #Attr.12;
-    let Test.5 = Index 1 #Attr.12;
+    let Test.6 = CoerceToTagId (Id 1) (Index 2) #Attr.12;
+    let Test.5 = CoerceToTagId (Id 1) (Index 1) #Attr.12;
     if Test.6 then
         let Test.24 = CallByName Num.26 Test.11 Test.5;
         ret Test.24;
diff --git a/compiler/test_mono/generated/specialize_lowlevel.txt b/compiler/test_mono/generated/specialize_lowlevel.txt
index 6f36920266..cd81b26370 100644
--- a/compiler/test_mono/generated/specialize_lowlevel.txt
+++ b/compiler/test_mono/generated/specialize_lowlevel.txt
@@ -7,12 +7,12 @@ procedure Num.26 (#Attr.2, #Attr.3):
     ret Test.21;
 
 procedure Test.6 (Test.8, #Attr.12):
-    let Test.4 = Index 1 #Attr.12;
+    let Test.4 = CoerceToTagId (Id 0) (Index 1) #Attr.12;
     let Test.25 = CallByName Num.24 Test.8 Test.4;
     ret Test.25;
 
 procedure Test.7 (Test.9, #Attr.12):
-    let Test.5 = Index 1 #Attr.12;
+    let Test.5 = CoerceToTagId (Id 1) (Index 1) #Attr.12;
     let Test.20 = CallByName Num.26 Test.9 Test.5;
     ret Test.20;