diff --git a/compiler/mono/src/layout.rs b/compiler/mono/src/layout.rs
index 5cee9a52a6..4f0b7ef1fe 100644
--- a/compiler/mono/src/layout.rs
+++ b/compiler/mono/src/layout.rs
@@ -1994,7 +1994,15 @@ pub fn union_sorted_tags<'a>(
 
     let mut tags_vec = std::vec::Vec::new();
     let result = match roc_types::pretty_print::chase_ext_tag_union(subs, var, &mut tags_vec) {
-        Ok(()) | Err((_, Content::FlexVar(_))) | Err((_, Content::RecursionVar { .. })) => {
+        Ok(())
+        // Admit type variables in the extension for now. This may come from things that never got
+        // monomorphized, like in
+        //   x : [ A ]*
+        //   x = A
+        //   x
+        // In such cases it's fine to drop the variable. We may be proven wrong in the future...
+        | Err((_, Content::FlexVar(_) | Content::RigidVar(_)))
+        | Err((_, Content::RecursionVar { .. })) => {
             let opt_rec_var = get_recursion_var(subs, var);
             union_sorted_tags_help(arena, tags_vec, opt_rec_var, subs, target_info)
         }
@@ -2592,7 +2600,7 @@ pub fn ext_var_is_empty_tag_union(subs: &Subs, ext_var: Variable) -> bool {
     // the ext_var is empty
     let mut ext_fields = std::vec::Vec::new();
     match roc_types::pretty_print::chase_ext_tag_union(subs, ext_var, &mut ext_fields) {
-        Ok(()) | Err((_, Content::FlexVar(_))) => ext_fields.is_empty(),
+        Ok(()) | Err((_, Content::FlexVar(_) | Content::RigidVar(_))) => ext_fields.is_empty(),
         Err(content) => panic!("invalid content in ext_var: {:?}", content),
     }
 }
diff --git a/compiler/test_gen/src/gen_tags.rs b/compiler/test_gen/src/gen_tags.rs
index 4cab64ec87..8a5e2d276a 100644
--- a/compiler/test_gen/src/gen_tags.rs
+++ b/compiler/test_gen/src/gen_tags.rs
@@ -1548,3 +1548,19 @@ fn issue_1162() {
         u8
     )
 }
+
+#[test]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
+fn polymorphic_tag() {
+    assert_evals_to!(
+        indoc!(
+            r#"
+            x : [ Y U8 ]*
+            x = Y 3
+            x
+            "#
+        ),
+        3, // Y is a newtype, it gets unwrapped
+        u8
+    )
+}