diff --git a/hkmc2/shared/src/main/scala/hkmc2/codegen/js/JSBuilder.scala b/hkmc2/shared/src/main/scala/hkmc2/codegen/js/JSBuilder.scala
index f3734d305..3a6bd6b54 100644
--- a/hkmc2/shared/src/main/scala/hkmc2/codegen/js/JSBuilder.scala
+++ b/hkmc2/shared/src/main/scala/hkmc2/codegen/js/JSBuilder.scala
@@ -51,7 +51,7 @@ class JSBuilder(using Elaborator.State, Elaborator.Ctx) extends CodeBuilder:
       case S(owner) =>
         doc"${result(Value.This(owner))}.${
           if (ts.k is syntax.LetBind) && !owner.isInstanceOf[semantics.TopLevelSymbol]
-          then "#" + ts.id.name
+          then "#" + owner.privatesScope.lookup_!(ts)
           else ts.id.name
         }"
       case N => summon[Scope].lookup_!(ts)
@@ -157,12 +157,18 @@ class JSBuilder(using Elaborator.State, Elaborator.Ctx) extends CodeBuilder:
             // * Note: `_pubFlds` is not used because in JS, fields are not declared
             val clsParams = paramsOpt.fold(Nil)(_.paramSyms)
             val ctorParams = clsParams.map(p => p -> scope.allocateName(p))
+            val privs =
+              val scp = isym.asInstanceOf[InnerSymbol].privatesScope
+              privFlds.map: fld =>
+                  val nme = scp.allocateName(fld)
+                  doc" # #$nme;"
+                .mkDocument(doc"")
             val preCtorCode = ctorParams.foldLeft(body(preCtor)):
               case (acc, (sym, nme)) =>
                 doc"$acc # this.${sym.name} = $nme;"
             val ctorCode = doc"$preCtorCode${body(ctor)}"
             val clsJS = doc"class ${sym.nme}${par.map(p => s" extends ${result(p)}").getOrElse("")} { #{ ${
-                privFlds.map(f => doc" # #${f.nme};").mkDocument(doc"")
+                privs
               } # constructor(${
                 ctorParams.unzip._2.mkDocument(", ")
               }) ${ braced(ctorCode) }${
diff --git a/hkmc2/shared/src/main/scala/hkmc2/semantics/Symbol.scala b/hkmc2/shared/src/main/scala/hkmc2/semantics/Symbol.scala
index 93c851dff..d91404bb4 100644
--- a/hkmc2/shared/src/main/scala/hkmc2/semantics/Symbol.scala
+++ b/hkmc2/shared/src/main/scala/hkmc2/semantics/Symbol.scala
@@ -6,6 +6,7 @@ import scala.collection.mutable.{Set => MutSet}
 
 import mlscript.utils.*, shorthands.*
 import syntax.*
+import hkmc2.utils.*
 
 import Elaborator.State
 import Tree.Ident
@@ -198,7 +199,8 @@ sealed trait ClassLikeSymbol extends Symbol:
   * One overloaded `BlockMemberSymbol` may correspond to multiple `InnerSymbol`s
   * A `Ref(_: InnerSymbol)` represents a `this`-like reference to the current object. */
   // TODO prevent from appearing in Ref
-sealed trait InnerSymbol extends Symbol:
+sealed trait InnerSymbol(using State) extends Symbol:
+  val privatesScope: Scope = Scope.empty // * Scope for private members of this symbol
   def subst(using SymbolSubst): InnerSymbol
 
 class ClassSymbol(val tree: Tree.TypeDef, val id: Tree.Ident)(using State)
diff --git a/hkmc2/shared/src/test/mlscript/backlog/ToTriage.mls b/hkmc2/shared/src/test/mlscript/backlog/ToTriage.mls
index 737f6a0f4..92bac09fd 100644
--- a/hkmc2/shared/src/test/mlscript/backlog/ToTriage.mls
+++ b/hkmc2/shared/src/test/mlscript/backlog/ToTriage.mls
@@ -223,3 +223,42 @@ fun main() =
 
 // ——— ——— ———
 
+// * Objects should not be allowed to have parameters...
+// * Or these parameters should have default values.
+
+:sjs
+object Cls(x) with
+  fun huh = x
+//│ JS (unsanitized):
+//│ let Cls1;
+//│ const Cls$class = class Cls {
+//│   constructor(x1) {
+//│     this.x = x1;
+//│   }
+//│   get huh() {
+//│     return this.x;
+//│   }
+//│   toString() { return "Cls(" + this.x + ")"; }
+//│ }; Cls1 = new Cls$class;
+//│ Cls1.class = Cls$class;
+//│ null
+
+:e
+Cls.x
+//│ ╔══[ERROR] Object 'Cls' does not contain member 'x'
+//│ ║  l.247: 	Cls.x
+//│ ╙──       	   ^^
+//│ ═══[RUNTIME ERROR] Error: Access to required field 'x' yielded 'undefined'
+
+:fixme
+Cls.huh
+//│ ═══[RUNTIME ERROR] Error: Access to required field 'huh' yielded 'undefined'
+
+let c = new Cls(123)
+//│ c = Cls { x: 123 }
+
+c.x
+//│ = 123
+
+// ——— ——— ———
+
diff --git a/hkmc2/shared/src/test/mlscript/codegen/Hygiene.mls b/hkmc2/shared/src/test/mlscript/codegen/Hygiene.mls
index 91f20bd80..87a909f6f 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/Hygiene.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/Hygiene.mls
@@ -82,15 +82,61 @@ Test.x
 //│ = 1
 
 
-:fixme
 module Test with
   let x = 1
   let f = () => x
   let x = 2
-  log(f())
-//│ > let Test7;try { const Test$class2 = class Test {   #x;   #f;   #x;   constructor() {     let selRes1, tmp, tmp1;     this.#x = 1;     this.#f = (...args) => {       globalThis.Predef.checkArgs("", 0, true, args.length);       return this.#x;     };     this.#x = 2;     selRes1 = globalThis.log;     if (selRes1 === undefined) {       throw new globalThis.Error("Access to required field 'log' yielded 'undefined'");     } else {       tmp = selRes1;     }     tmp1 = this.#f() ?? null;     tmp(tmp1) ?? null   }   toString() { return "Test"; } }; Test7 = new Test$class2; Test7.class = Test$class2; null } catch (e) { console.log('\u200B' + e + '\u200B'); }
-//│ >                                                                  ^
-//│ ═══[COMPILATION ERROR] [Uncaught SyntaxError] Identifier '#x' has already been declared
+  print(f())
+//│ > 1
+
+
+:sjs
+class Cls(x) with
+  let x += 1
+  fun foo = x
+  let x *= 2
+  fun bar = x
+  print(this.x, x)
+//│ JS (unsanitized):
+//│ let Cls1;
+//│ Cls1 = function Cls(x3) { return new Cls.class(x3); };
+//│ Cls1.class = class Cls {
+//│   #x;
+//│   #x1;
+//│   constructor(x2) {
+//│     this.x = x2;
+//│     let tmp, tmp1;
+//│     tmp = this.x + 1;
+//│     this.#x = tmp;
+//│     tmp1 = this.#x * 2;
+//│     this.#x1 = tmp1;
+//│     Predef.print(this.x, this.#x1)
+//│   }
+//│   get foo() {
+//│     return this.#x;
+//│   } 
+//│   get bar() {
+//│     return this.#x1;
+//│   }
+//│   toString() { return "Cls(" + this.x + ")"; }
+//│ };
+//│ null
+
+let cls = Cls(10)
+//│ > 10 22
+//│ cls = Cls { x: 10 }
+
+:expect 10
+cls.x
+//│ = 10
+
+:expect 11
+cls.foo
+//│ = 11
+
+:expect 22
+cls.bar
+//│ = 22
 
 
 fun foo() =
diff --git a/hkmc2/shared/src/test/mlscript/codegen/ReboundLet.mls b/hkmc2/shared/src/test/mlscript/codegen/ReboundLet.mls
index 28966ca99..6a9160456 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/ReboundLet.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/ReboundLet.mls
@@ -13,11 +13,6 @@ foo()
 //│ = 1
 
 
-
-// FIXME should pick a different private field name for each `x`:
-
-
-
 let x = 1
 let f = () => x
 //│ f = [Function: f]
@@ -33,9 +28,9 @@ f()
 //│ = 1
 
 
+// * Notice that we pick a different private field name for each `x`
 
-:fixme
-class Foo with
+object Foo with
   let x = 1
   let f = () => x
   fun g() = x
@@ -44,9 +39,9 @@ class Foo with
   print(x)
   print(f())
   print(g())
-//│ > let Foo1;try { Foo1 = class Foo {   #x;   #f;   #x;   constructor() {     let tmp, tmp1, tmp2, tmp3, tmp4, tmp5;     this.#x = 1;     this.#f = (...args) => {       globalThis.Predef.checkArgs("", 0, true, args.length);       return this.#x;     };     tmp = this.#f() ?? null;     tmp1 = Predef.print(tmp);     this.#x = 2;     tmp2 = Predef.print(this.#x);     tmp3 = this.#f() ?? null;     tmp4 = Predef.print(tmp3);     tmp5 = this.g();     Predef.print(tmp5)   }   g(...args) {     globalThis.Predef.checkArgs("g", 0, true, args.length);     return this.#x;   }   toString() { return "Foo"; } }; null } catch (e) { console.log('\u200B' + e + '\u200B'); }
-//│ >                                                   ^
-//│ ═══[COMPILATION ERROR] [Uncaught SyntaxError] Identifier '#x' has already been declared
-
+//│ > 1
+//│ > 2
+//│ > 1
+//│ > 1