diff --git a/compiler/can/src/annotation.rs b/compiler/can/src/annotation.rs
index 38f5d99b63..ee5369dd4f 100644
--- a/compiler/can/src/annotation.rs
+++ b/compiler/can/src/annotation.rs
@@ -7,7 +7,7 @@ use roc_module::symbol::{IdentIds, ModuleId, Symbol};
 use roc_parse::ast::{AssignedField, Pattern, Tag, TypeAnnotation, TypeHeader};
 use roc_region::all::{Loc, Region};
 use roc_types::subs::{VarStore, Variable};
-use roc_types::types::{Alias, AliasKind, LambdaSet, Problem, RecordField, Type};
+use roc_types::types::{Alias, AliasKind, LambdaSet, Problem, RecordField, Type, TypeExtension};
 
 #[derive(Clone, Debug, PartialEq)]
 pub struct Annotation {
@@ -542,7 +542,7 @@ fn can_annotation_help(
                         // just `a` does not mean the same as `{}a`, so even
                         // if there are no fields, still make this a `Record`,
                         // not an EmptyRec
-                        Type::Record(Default::default(), Box::new(ext_type))
+                        Type::Record(Default::default(), TypeExtension::from_type(ext_type))
                     }
 
                     None => Type::EmptyRec,
@@ -559,7 +559,7 @@ fn can_annotation_help(
                     references,
                 );
 
-                Type::Record(field_types, Box::new(ext_type))
+                Type::Record(field_types, TypeExtension::from_type(ext_type))
             }
         }
         TagUnion { tags, ext, .. } => {
@@ -580,7 +580,7 @@ fn can_annotation_help(
                         // just `a` does not mean the same as `{}a`, so even
                         // if there are no fields, still make this a `Record`,
                         // not an EmptyRec
-                        Type::TagUnion(Default::default(), Box::new(ext_type))
+                        Type::TagUnion(Default::default(), TypeExtension::from_type(ext_type))
                     }
 
                     None => Type::EmptyTagUnion,
@@ -602,7 +602,7 @@ fn can_annotation_help(
                 // in theory we save a lot of time by sorting once here
                 insertion_sort_by(&mut tag_types, |a, b| a.0.cmp(&b.0));
 
-                Type::TagUnion(tag_types, Box::new(ext_type))
+                Type::TagUnion(tag_types, TypeExtension::from_type(ext_type))
             }
         }
         SpaceBefore(nested, _) | SpaceAfter(nested, _) => can_annotation_help(
diff --git a/compiler/can/src/effect_module.rs b/compiler/can/src/effect_module.rs
index 92fd123ab4..1c2f76d951 100644
--- a/compiler/can/src/effect_module.rs
+++ b/compiler/can/src/effect_module.rs
@@ -10,7 +10,7 @@ use roc_module::ident::TagName;
 use roc_module::symbol::Symbol;
 use roc_region::all::{Loc, Region};
 use roc_types::subs::{VarStore, Variable};
-use roc_types::types::{AliasKind, Type};
+use roc_types::types::{AliasKind, Type, TypeExtension};
 
 #[derive(Default, Clone, Copy)]
 pub(crate) struct HostedGeneratedFunctions {
@@ -1111,7 +1111,7 @@ fn build_effect_loop(
                     (step_tag_name, vec![Type::Variable(var_a)]),
                     (done_tag_name, vec![Type::Variable(var_b)]),
                 ],
-                Box::new(Type::EmptyTagUnion),
+                TypeExtension::Closed,
             )
         };
 
@@ -1129,7 +1129,7 @@ fn build_effect_loop(
                             Box::new(state_type.clone()),
                         )],
                     )],
-                    Box::new(Type::EmptyTagUnion),
+                    TypeExtension::Closed,
                 )
             };
 
@@ -1571,7 +1571,7 @@ fn build_effect_alias(
                     Box::new(a_type),
                 )],
             )],
-            Box::new(Type::EmptyTagUnion),
+            TypeExtension::Closed,
         )
     };
 
@@ -1600,7 +1600,7 @@ pub fn build_effect_actual(
                 Box::new(a_type),
             )],
         )],
-        Box::new(Type::EmptyTagUnion),
+        TypeExtension::Closed,
     )
 }
 
diff --git a/compiler/types/src/types.rs b/compiler/types/src/types.rs
index 2cbdac3fa5..fcd58f2f0e 100644
--- a/compiler/types/src/types.rs
+++ b/compiler/types/src/types.rs
@@ -219,6 +219,15 @@ pub enum TypeExtension {
     Closed,
 }
 
+impl TypeExtension {
+    pub fn from_type(typ: Type) -> Self {
+        match typ {
+            Type::EmptyTagUnion | Type::EmptyRec => Self::Closed,
+            _ => Self::Open(Box::new(typ)),
+        }
+    }
+}
+
 impl IntoIterator for TypeExtension {
     type Item = Box<Type>;