diff --git a/changes/untagged-bool-payload-match.fix.md b/changes/untagged-bool-payload-match.fix.md
new file mode 100644
index 0000000000..1e0eb099a4
--- /dev/null
+++ b/changes/untagged-bool-payload-match.fix.md
@@ -0,0 +1 @@
+- Fix matching a bool payload of an untagged variant beside a bool literal case in a match that does not name every case.
diff --git a/compiler/core/js_exp_make.ml b/compiler/core/js_exp_make.ml
index 31b6a1dd78..f65284cb24 100644
--- a/compiler/core/js_exp_make.ml
+++ b/compiler/core/js_exp_make.ml
@@ -1059,7 +1059,21 @@ let rec simplify_and_ ~n (e1 : t) (e2 : t) : t option =
               {expression_desc = Typeof {expression_desc = Var ia}},
               {expression_desc = Str "boolean"} ) )
         when Js_op_util.same_vident ia ib ->
-        Some {expression_desc = Bool (not b); comment = None; source_loc = None}
+        (* A boolean other than [b] is [!b] *)
+        Some
+          {
+            expression_desc =
+              Bin
+                ( EqEqEq,
+                  {expression_desc = Var ib; comment = None; source_loc = None},
+                  {
+                    expression_desc = Bool (not b);
+                    comment = None;
+                    source_loc = None;
+                  } );
+            comment = None;
+            source_loc = None;
+          }
       | ( Bin
             ( EqEqEq,
               {expression_desc = Typeof {expression_desc = Var ia}},
diff --git a/tests/tests/src/untagged_bool_payload_test.mjs b/tests/tests/src/untagged_bool_payload_test.mjs
new file mode 100644
index 0000000000..b00d9f2413
--- /dev/null
+++ b/tests/tests/src/untagged_bool_payload_test.mjs
@@ -0,0 +1,44 @@
+// Generated by ReScript, PLEASE EDIT WITH CARE
+
+import * as Mocha from "mocha";
+import * as Test_utils from "./test_utils.mjs";
+
+function id(x) {
+  return x;
+}
+
+function trueKind(v) {
+  if (v !== false) {
+    return "other";
+  } else {
+    return "bool";
+  }
+}
+
+function falseKind(v) {
+  if (v !== true) {
+    return "other";
+  } else {
+    return "bool";
+  }
+}
+
+Mocha.describe("Untagged_bool_payload_test", () => {
+  Mocha.test("beside @as(true)", () => {
+    Test_utils.eq("File \"untagged_bool_payload_test.res\", line 26, characters 7-14", trueKind(id(false)), "bool");
+    Test_utils.eq("File \"untagged_bool_payload_test.res\", line 27, characters 7-14", trueKind(id(true)), "other");
+    Test_utils.eq("File \"untagged_bool_payload_test.res\", line 28, characters 7-14", trueKind(id(1)), "other");
+  });
+  Mocha.test("beside @as(false)", () => {
+    Test_utils.eq("File \"untagged_bool_payload_test.res\", line 32, characters 7-14", falseKind(id(true)), "bool");
+    Test_utils.eq("File \"untagged_bool_payload_test.res\", line 33, characters 7-14", falseKind(id(false)), "other");
+    Test_utils.eq("File \"untagged_bool_payload_test.res\", line 34, characters 7-14", falseKind(id(1)), "other");
+  });
+});
+
+export {
+  id,
+  trueKind,
+  falseKind,
+}
+/*  Not a pure module */
diff --git a/tests/tests/src/untagged_bool_payload_test.res b/tests/tests/src/untagged_bool_payload_test.res
new file mode 100644
index 0000000000..88e2ac7064
--- /dev/null
+++ b/tests/tests/src/untagged_bool_payload_test.res
@@ -0,0 +1,36 @@
+open Mocha
+open Test_utils
+
+// A bool payload receives the booleans that are not literal cases, also in a
+// match that does not name every case (#9035)
+
+@unboxed type withTrue = | @as(true) LitTrue | TrueBool(bool) | TrueInt(int)
+@unboxed type withFalse = | @as(false) LitFalse | FalseBool(bool) | FalseInt(int)
+
+@inline(never) let id = x => x
+
+let trueKind = (v: withTrue) =>
+  switch v {
+  | TrueBool(_) => "bool"
+  | _ => "other"
+  }
+
+let falseKind = (v: withFalse) =>
+  switch v {
+  | FalseBool(_) => "bool"
+  | _ => "other"
+  }
+
+describe(__MODULE__, () => {
+  test("beside @as(true)", () => {
+    eq(__LOC__, trueKind(id(TrueBool(false))), "bool")
+    eq(__LOC__, trueKind(id(LitTrue)), "other")
+    eq(__LOC__, trueKind(id(TrueInt(1))), "other")
+  })
+
+  test("beside @as(false)", () => {
+    eq(__LOC__, falseKind(id(FalseBool(true))), "bool")
+    eq(__LOC__, falseKind(id(LitFalse)), "other")
+    eq(__LOC__, falseKind(id(FalseInt(1))), "other")
+  })
+})