diff --git a/CHANGELOG.md b/CHANGELOG.md
index bc4ff3c699..1e014fd81c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -23,6 +23,7 @@
 - Support renaming object fields of `@obj` external ppx with `@as` attribute. [#6391](https://github.com/rescript-lang/rescript-compiler/pull/6412)
 - Add builtin abstract types for File and Blob APIs. https://github.com/rescript-lang/rescript-compiler/pull/6383
 - Untagged variants: Support `promise`, RegExes, Dates, File and Blob. https://github.com/rescript-lang/rescript-compiler/pull/6383
+- Untagged variants: Support `bool`. https://github.com/rescript-lang/rescript-compiler/pull/6368
 - Support aliased types as payloads to untagged variants. https://github.com/rescript-lang/rescript-compiler/pull/6394
 
 #### :boom: Breaking Change
diff --git a/jscomp/build_tests/unboxed_bool_with_const/bsconfig.json b/jscomp/build_tests/unboxed_bool_with_const/bsconfig.json
new file mode 100644
index 0000000000..1cbcace50a
--- /dev/null
+++ b/jscomp/build_tests/unboxed_bool_with_const/bsconfig.json
@@ -0,0 +1,15 @@
+{
+  "name": "unboxed_bool_with_const",
+  "version": "0.1.0",
+  "sources": [
+    {
+      "dir": "src",
+      "subdirs": true
+    }
+  ],
+  "package-specs": {
+    "module": "commonjs",
+    "in-source": true
+  },
+  "suffix": ".bs.js"
+}
diff --git a/jscomp/build_tests/unboxed_bool_with_const/input.js b/jscomp/build_tests/unboxed_bool_with_const/input.js
new file mode 100644
index 0000000000..4591fdadac
--- /dev/null
+++ b/jscomp/build_tests/unboxed_bool_with_const/input.js
@@ -0,0 +1,26 @@
+//@ts-check
+
+var cp = require("child_process");
+var assert = require("assert");
+var rescript_exe = require("../../../scripts/bin_path").rescript_exe;
+
+var out = cp.spawnSync(rescript_exe, {
+  cwd: __dirname,
+  encoding: "utf8",
+});
+
+assert.equal(
+  out.stdout.slice(out.stdout.indexOf("Main.res:3:3-14")),
+  `Main.res:3:3-14
+
+  1 │ @unboxed
+  2 │ type t<'a> =
+  3 │   | Bool(bool)
+  4 │   | @as(false) False
+  5 │   | @as(true) True
+
+  This untagged variant definition is invalid: At most one case can be a boolean type.
+
+FAILED: cannot make progress due to previous errors.
+`
+);
diff --git a/jscomp/build_tests/unboxed_bool_with_const/src/Main.res b/jscomp/build_tests/unboxed_bool_with_const/src/Main.res
new file mode 100644
index 0000000000..6ed5758e7e
--- /dev/null
+++ b/jscomp/build_tests/unboxed_bool_with_const/src/Main.res
@@ -0,0 +1,5 @@
+@unboxed
+type t<'a> =
+  | Bool(bool)
+  | @as(false) False
+  | @as(true) True
diff --git a/jscomp/core/js_exp_make.ml b/jscomp/core/js_exp_make.ml
index cc8b517bbe..a807fa6531 100644
--- a/jscomp/core/js_exp_make.ml
+++ b/jscomp/core/js_exp_make.ml
@@ -805,6 +805,7 @@ let tag_type = function
   | Undefined -> undefined
   | Untagged IntType -> str "number"
   | Untagged FloatType -> str "number"
+  | Untagged BooleanType -> str "boolean"
   | Untagged FunctionType -> str "function"
   | Untagged StringType -> str "string"
   | Untagged (InstanceType i) -> str (Ast_untagged_variants.Instance.to_string i) ~delim:DNoQuotes
diff --git a/jscomp/ml/ast_untagged_variants.ml b/jscomp/ml/ast_untagged_variants.ml
index 48a0e3ca3c..7f4e85532c 100644
--- a/jscomp/ml/ast_untagged_variants.ml
+++ b/jscomp/ml/ast_untagged_variants.ml
@@ -22,6 +22,7 @@ type untaggedError =
   | AtMostOneFunction
   | AtMostOneString
   | AtMostOneNumber
+  | AtMostOneBoolean
   | DuplicateLiteral of string
   | ConstructorMoreThanOneArg of string
 type error =
@@ -49,6 +50,7 @@ let report_error ppf =
       | AtMostOneInstance i -> "At most one case can be a " ^ (Instance.to_string i) ^ " type."
       | AtMostOneFunction -> "At most one case can be a function type."
       | AtMostOneString -> "At most one case can be a string type."
+      | AtMostOneBoolean -> "At most one case can be a boolean type."
       | AtMostOneNumber ->
         "At most one case can be a number type (int or float)."
       | DuplicateLiteral s -> "Duplicate literal " ^ s ^ "."
@@ -59,6 +61,7 @@ type block_type =
   | IntType
   | StringType
   | FloatType
+  | BooleanType
   | InstanceType of Instance.t
   | FunctionType
   | ObjectType
@@ -167,6 +170,8 @@ let get_block_type_from_typ ~env (t: Types.type_expr) : block_type option =
     Some IntType
   | {desc = Tconstr (path, _, _)} when Path.same path Predef.path_float ->
     Some FloatType
+  | {desc = Tconstr (path, _, _)} when Path.same path Predef.path_bool ->
+      Some BooleanType
   | ({desc = Tconstr _} as t) when Ast_uncurried_utils.typeIsUncurriedFun t ->
     Some FunctionType
   | {desc = Tarrow _} -> Some FunctionType
@@ -232,6 +237,7 @@ let checkInvariant ~isUntaggedDef ~(consts : (Location.t * tag) list)
   let objectTypes = ref 0 in
   let stringTypes = ref 0 in
   let numberTypes = ref 0 in
+  let booleanTypes = ref 0 in
   let unknownTypes = ref 0 in
   let addStringLiteral ~loc s =
     if StringSet.mem s !string_literals then
@@ -258,6 +264,10 @@ let checkInvariant ~isUntaggedDef ~(consts : (Location.t * tag) list)
       raise (Error (loc, InvalidUntaggedVariantDefinition AtMostOneString));
     if !numberTypes > 1 then
       raise (Error (loc, InvalidUntaggedVariantDefinition AtMostOneNumber));
+    if !booleanTypes > 1 then
+      raise (Error (loc, InvalidUntaggedVariantDefinition AtMostOneBoolean));
+    if !booleanTypes > 0 && (StringSet.mem "true" !nonstring_literals || StringSet.mem "false" !nonstring_literals) then
+      raise (Error (loc, InvalidUntaggedVariantDefinition AtMostOneBoolean));
     ()
   in
   Ext_list.rev_iter consts (fun (loc, literal) ->
@@ -267,34 +277,27 @@ let checkInvariant ~isUntaggedDef ~(consts : (Location.t * tag) list)
       | Some (Float f) -> addNonstringLiteral ~loc f
       | Some Null -> addNonstringLiteral ~loc "null"
       | Some Undefined -> addNonstringLiteral ~loc "undefined"
-      | Some (Bool b) ->
-        addNonstringLiteral ~loc (if b then "true" else "false")
+      | Some (Bool b) -> addNonstringLiteral ~loc (if b then "true" else "false")
       | Some (Untagged _) -> ()
       | None -> addStringLiteral ~loc literal.name);
   if isUntaggedDef then
     Ext_list.rev_iter blocks (fun (loc, block) ->
-        let name = block.tag.name in
-        match block.block_type with
-        | Some UnknownType ->
-          incr unknownTypes;
-          invariant loc name
-        | Some ObjectType ->
-          incr objectTypes;
-          invariant loc name
-        | Some (InstanceType i) ->
+      match block.block_type with
+      | Some block_type ->
+        (match block_type with
+        | UnknownType -> incr unknownTypes;
+        | ObjectType -> incr objectTypes;
+        | (InstanceType i) ->
           let count = Hashtbl.find_opt instanceTypes i |> Option.value ~default:0 in
           Hashtbl.replace instanceTypes i (count + 1);
-          invariant loc name
-        | Some FunctionType ->
-          incr functionTypes;
-          invariant loc name
-        | Some (IntType | FloatType) ->
-          incr numberTypes;
-          invariant loc name
-        | Some StringType ->
-          incr stringTypes;
-          invariant loc name
-        | None -> ())
+        | FunctionType -> incr functionTypes;
+        | (IntType | FloatType) -> incr numberTypes;
+        | BooleanType -> incr booleanTypes;
+        | StringType -> incr stringTypes;
+        );
+        invariant loc block.tag.name
+      | None -> ()
+    )
 
 let names_from_type_variant ?(isUntaggedDef = false) ~env
     (cstrs : Types.constructor_declaration list) =
@@ -353,6 +356,7 @@ module DynamicChecks = struct
   let function_ = Untagged FunctionType |> tag_type
   let string = Untagged StringType |> tag_type
   let number = Untagged IntType |> tag_type
+  let boolean = Untagged BooleanType |> tag_type
 
   let ( == ) x y = bin EqEqEq x y
   let ( != ) x y = bin NotEqEq x y
@@ -371,6 +375,11 @@ module DynamicChecks = struct
         | Int _ | Float _ -> true
         | _ -> false)
     in
+    let literals_overlaps_with_boolean () =
+      Ext_list.exists literal_cases (function
+        | Bool _ -> true
+        | _ -> false)
+    in
     let literals_overlaps_with_object () =
       Ext_list.exists literal_cases (function
         | Null -> true
@@ -386,6 +395,8 @@ module DynamicChecks = struct
         typeof e != number
       | FloatType when literals_overlaps_with_number () = false ->
         typeof e != number
+      | BooleanType when literals_overlaps_with_boolean () = false ->
+        typeof e != boolean
       | InstanceType i -> not (is_instance i e)
       | FunctionType -> typeof e != function_
       | ObjectType when literals_overlaps_with_object () = false ->
@@ -394,6 +405,7 @@ module DynamicChecks = struct
       | StringType (* overlap *)
       | IntType (* overlap *)
       | FloatType (* overlap *)
+      | BooleanType (* overlap *)
       | UnknownType -> (
         (* We don't know the type of unknown, so we need to express:
            this is not one of the literals *)
@@ -434,7 +446,7 @@ module DynamicChecks = struct
   let add_runtime_type_check ~tag_type ~(block_cases : block_type list) x y =
     let instances = Ext_list.filter_map block_cases (function InstanceType i -> Some i | _ -> None) in
     match tag_type with
-    | Untagged (IntType | StringType | FloatType | FunctionType) ->
+    | Untagged (IntType | StringType | FloatType | BooleanType | FunctionType) ->
       typeof y == x
     | Untagged ObjectType ->
       if instances <> [] then
diff --git a/jscomp/test/variantsMatching.gen.tsx b/jscomp/test/variantsMatching.gen.tsx
index 8718551676..023a483cec 100644
--- a/jscomp/test/variantsMatching.gen.tsx
+++ b/jscomp/test/variantsMatching.gen.tsx
@@ -19,3 +19,6 @@ export type MyNullable_t<a> = null | undefined | a;
 
 // tslint:disable-next-line:interface-over-type-literal
 export type MyNullableExtended_t<a> = null | undefined | "WhyNotAnotherOne" | a;
+
+// tslint:disable-next-line:interface-over-type-literal
+export type UntaggedWithBool_t = string | number | boolean | string;
diff --git a/jscomp/test/variantsMatching.js b/jscomp/test/variantsMatching.js
index 859d348f0e..2573077d54 100644
--- a/jscomp/test/variantsMatching.js
+++ b/jscomp/test/variantsMatching.js
@@ -389,6 +389,28 @@ var CustomTagNotInline = {
   b: CustomTagNotInline_b
 };
 
+function classify(x) {
+  switch (typeof x) {
+    case "string" :
+        return "string";
+    case "number" :
+        return "int";
+    case "boolean" :
+        if (x) {
+          return "true";
+        } else {
+          return "boolean";
+        }
+    case "object" :
+        return "Object" + x.name;
+    
+  }
+}
+
+var UntaggedWithBool = {
+  classify: classify
+};
+
 exports.toEnum = toEnum;
 exports.toString = toString;
 exports.bar = bar;
@@ -406,4 +428,5 @@ exports.MyNullable = MyNullable;
 exports.MyNullableExtended = MyNullableExtended;
 exports.TaggedUnions = TaggedUnions;
 exports.CustomTagNotInline = CustomTagNotInline;
+exports.UntaggedWithBool = UntaggedWithBool;
 /* expectSeven Not a pure module */
diff --git a/jscomp/test/variantsMatching.res b/jscomp/test/variantsMatching.res
index f8b3efd113..aca376049f 100644
--- a/jscomp/test/variantsMatching.res
+++ b/jscomp/test/variantsMatching.res
@@ -272,3 +272,17 @@ module CustomTagNotInline = {
   let a = A(10)
   let b = B(20)
 }
+
+module UntaggedWithBool = {
+  @unboxed @genType
+  type t = String(string) | Float(float) | Bool(bool) | Object({name: string})
+
+  let classify = x =>
+    switch x {
+    | String(_) => "string"
+    | Float(_) => "int"
+    | Bool(true) => "true"
+    | Bool(_) => "boolean"
+    | Object({name}) => "Object" ++ name
+    }
+}