diff --git a/CHANGELOG.md b/CHANGELOG.md
index 81c3e2b34..b677f0720 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -28,7 +28,7 @@ Changes to hax-lib:
  - Lean lib: add new setup for `bv_decide` (#1828)
  - Lean lib: base specs on mathematical integers (#1829)
  - Lean lib: represent `usize` via a copy of `UInt64` (#1829)
- - Lean lib: Add support for while loops (#1857)
+ - Lean lib: Add support for while loops (#1857, #1863)
 
 Changes to the Lean backend:
  - Support for constants with arbitrary computation (#1738)
diff --git a/hax-lib/proof-libs/lean/Hax/Lib.lean b/hax-lib/proof-libs/lean/Hax/Lib.lean
index 99ff6533c..ec28b95fe 100644
--- a/hax-lib/proof-libs/lean/Hax/Lib.lean
+++ b/hax-lib/proof-libs/lean/Hax/Lib.lean
@@ -333,19 +333,19 @@ macro "declare_comparison_specs" s:(&"signed" <|> &"unsigned") typeName:ident wi
         mvcgen [ne]; rw [← @Bool.coe_iff_coe]; simp [x.toInt_inj]
 
       @[spec]
-      def lt_spec (x y : $typeName) : ⦃ ⌜ True ⌝ ⦄ lt x y ⦃ ⇓ r => ⌜ r = (x.toInt < y.toInt) ⌝ ⦄ := by
+      def lt_spec (x y : $typeName) : ⦃ ⌜ True ⌝ ⦄ lt x y ⦃ ⇓ r => ⌜ r = decide (x.toInt < y.toInt) ⌝ ⦄ := by
         mvcgen [lt]; simp [x.lt_iff_toInt_lt]
 
       @[spec]
-      def le_spec (x y : $typeName) : ⦃ ⌜ True ⌝ ⦄ le x y ⦃ ⇓ r => ⌜ r = (x.toInt ≤ y.toInt) ⌝ ⦄ := by
+      def le_spec (x y : $typeName) : ⦃ ⌜ True ⌝ ⦄ le x y ⦃ ⇓ r => ⌜ r = decide (x.toInt ≤ y.toInt) ⌝ ⦄ := by
         mvcgen [le]; simp [x.le_iff_toInt_le]
 
       @[spec]
-      def gt_spec (x y : $typeName) : ⦃ ⌜ True ⌝ ⦄ gt x y ⦃ ⇓ r => ⌜ r = (x.toInt > y.toInt ) ⌝ ⦄ := by
+      def gt_spec (x y : $typeName) : ⦃ ⌜ True ⌝ ⦄ gt x y ⦃ ⇓ r => ⌜ r = decide (x.toInt > y.toInt ) ⌝ ⦄ := by
         mvcgen [gt]; simp [y.lt_iff_toInt_lt]
 
       @[spec]
-      def ge_spec (x y : $typeName) : ⦃ ⌜ True ⌝ ⦄ ge x y ⦃ ⇓ r => ⌜ r = (x.toInt ≥ y.toInt) ⌝ ⦄ := by
+      def ge_spec (x y : $typeName) : ⦃ ⌜ True ⌝ ⦄ ge x y ⦃ ⇓ r => ⌜ r = decide (x.toInt ≥ y.toInt) ⌝ ⦄ := by
         mvcgen [ge]; simp [y.le_iff_toInt_le]
 
       end $typeName
@@ -362,20 +362,20 @@ macro "declare_comparison_specs" s:(&"signed" <|> &"unsigned") typeName:ident wi
         mvcgen [ne]; rw [← @Bool.coe_iff_coe]; simp [x.toNat_inj]
 
       @[spec]
-      def lt_spec (x y : $typeName) : ⦃ ⌜ True ⌝ ⦄ lt x y ⦃ ⇓ r => ⌜ r = (x.toNat < y.toNat) ⌝ ⦄ := by
-        mvcgen [lt]; simp [x.lt_iff_toNat_lt]
+      def lt_spec (x y : $typeName) : ⦃ ⌜ True ⌝ ⦄ lt x y ⦃ ⇓ r => ⌜ r = decide (x.toNat < y.toNat) ⌝ ⦄ := by
+        mvcgen [lt]
 
       @[spec]
-      def le_spec (x y : $typeName) : ⦃ ⌜ True ⌝ ⦄ le x y ⦃ ⇓ r => ⌜ r = (x.toNat ≤ y.toNat) ⌝ ⦄ := by
-        mvcgen [le]; simp [x.le_iff_toNat_le]
+      def le_spec (x y : $typeName) : ⦃ ⌜ True ⌝ ⦄ le x y ⦃ ⇓ r => ⌜ r = decide (x.toNat ≤ y.toNat) ⌝ ⦄ := by
+        mvcgen [le]
 
       @[spec]
-      def gt_spec (x y : $typeName) : ⦃ ⌜ True ⌝ ⦄ gt x y ⦃ ⇓ r => ⌜ r = (x.toNat > y.toNat ) ⌝ ⦄ := by
-        mvcgen [gt]; simp [y.lt_iff_toNat_lt]
+      def gt_spec (x y : $typeName) : ⦃ ⌜ True ⌝ ⦄ gt x y ⦃ ⇓ r => ⌜ r = decide (x.toNat > y.toNat ) ⌝ ⦄ := by
+        mvcgen [gt]
 
       @[spec]
-      def ge_spec (x y : $typeName) : ⦃ ⌜ True ⌝ ⦄ ge x y ⦃ ⇓ r => ⌜ r = (x.toNat ≥ y.toNat) ⌝ ⦄ := by
-        mvcgen [ge]; simp [y.le_iff_toNat_le]
+      def ge_spec (x y : $typeName) : ⦃ ⌜ True ⌝ ⦄ ge x y ⦃ ⇓ r => ⌜ r = decide (x.toNat ≥ y.toNat) ⌝ ⦄ := by
+        mvcgen [ge]
 
       end $typeName
   )
@@ -747,12 +747,15 @@ def Rust_primitives.Hax.while_loop {β : Type}
     (init : β)
     (body : β -> RustM β)
     (pureInv:
-        {i : β -> Prop // ∀ b, ⦃⌜ True ⌝⦄ inv b ⦃⇓ r => ⌜ (i b) = r ⌝⦄} := by
+        {i : β -> Prop // ∀ b, ⦃⌜ True ⌝⦄ inv b ⦃⇓ r => ⌜ r = (i b) ⌝⦄} := by
       constructor; intro; mvcgen)
     (pureTermination :
-        {t : β -> Nat // ∀ b, ⦃⌜ True ⌝⦄ termination b ⦃⇓ r => ⌜ Int.ofNat (t b) = r ⌝⦄} := by
+        {t : β -> Nat // ∀ b, ⦃⌜ True ⌝⦄ termination b ⦃⇓ r => ⌜ r = Int.ofNat (t b) ⌝⦄} := by
+      constructor; intro; mvcgen)
+    (pureCond :
+        {c : β -> Bool // ∀ b, ⦃⌜ pureInv.val b ⌝⦄ cond b ⦃⇓ r => ⌜ r = c b ⌝⦄} := by
       constructor; intro; mvcgen) : RustM β :=
-  Loop.MonoLoopCombinator.while_loop Loop.mk cond init body
+  Loop.MonoLoopCombinator.while_loop Loop.mk pureCond.val init body
 
 @[spec]
 theorem Rust_primitives.Hax.while_loop.spec {β : Type}
@@ -761,25 +764,19 @@ theorem Rust_primitives.Hax.while_loop.spec {β : Type}
     (termination: β → RustM Hax_lib.Int.Int)
     (init : β)
     (body : β -> RustM β)
-    (pureInv: {i : β -> Prop // ∀ b, ⦃⌜ True ⌝⦄ inv b ⦃⇓ r => ⌜ (i b) = r ⌝⦄})
+    (pureInv: {i : β -> Prop // ∀ b, ⦃⌜ True ⌝⦄ inv b ⦃⇓ r => ⌜ r = (i b) ⌝⦄})
     (pureTermination :
-      {t : β -> Nat // ∀ b, ⦃⌜ True ⌝⦄ termination b ⦃⇓ r => ⌜ Int.ofNat (t b) = r ⌝⦄})
-    (step : ∀ (b : β),
-      ⦃⌜pureInv.val b⌝⦄
-        do
-          if ← cond b
-          then ForInStep.yield (← body b)
-          else ForInStep.done b
-      ⦃⇓ r =>
-        match r with
-        | ForInStep.yield b' =>
-          spred(⌜ pureTermination.val b' < pureTermination.val b ⌝ ∧ ⌜ pureInv.val b' ⌝)
-        | ForInStep.done b' =>
-          ⌜ pureInv.val b' ⌝⦄) :
+      {t : β -> Nat // ∀ b, ⦃⌜ True ⌝⦄ termination b ⦃⇓ r => ⌜ r = Int.ofNat (t b) ⌝⦄})
+    (pureCond : {c : β -> Bool // ∀ b, ⦃⌜ pureInv.val b ⌝⦄ cond b ⦃⇓ r => ⌜ r = c b ⌝⦄})
+    (step :
+      ∀ (b : β), pureCond.val b →
+        ⦃⌜ pureInv.val b ⌝⦄
+          body b
+        ⦃⇓ b' => spred(⌜ pureTermination.val b' < pureTermination.val b ⌝ ∧ ⌜ pureInv.val b' ⌝)⦄ ) :
     ⦃⌜ pureInv.val init ⌝⦄
-      while_loop inv cond termination init body pureInv pureTermination
-    ⦃⇓ r => ⌜ pureInv.val r ⌝⦄ :=
-  Spec.MonoLoopCombinator.while_loop init Loop.mk cond body pureInv pureTermination step
+      while_loop inv cond termination init body pureInv pureTermination pureCond
+    ⦃⇓ r => ⌜ pureInv.val r ∧ ¬ pureCond.val r ⌝⦄ :=
+  Spec.MonoLoopCombinator.while_loop init Loop.mk pureCond.val body pureInv pureTermination step
 
 end Loop
 /-
diff --git a/hax-lib/proof-libs/lean/Hax/MissingLean/Init/While.lean b/hax-lib/proof-libs/lean/Hax/MissingLean/Init/While.lean
index e13f951b8..dadd508eb 100644
--- a/hax-lib/proof-libs/lean/Hax/MissingLean/Init/While.lean
+++ b/hax-lib/proof-libs/lean/Hax/MissingLean/Init/While.lean
@@ -36,12 +36,12 @@ def Loop.MonoLoopCombinator.forIn {β : Type u} {m : Type u → Type v} [Monad m
 def Loop.MonoLoopCombinator.while_loop  {m} {ps : PostShape} {β: Type}
     [Monad m] [∀ α, Order.CCPO (m α)] [WPMonad m ps]
     (loop : Loop)
-    (cond: β → m Bool)
+    (cond: β → Bool)
     (init : β)
     (body : β -> m β)
     [∀ f : Unit → β → m (ForInStep β), Loop.MonoLoopCombinator f] : m β :=
   Loop.MonoLoopCombinator.forIn loop init fun () s => do
-    if ← cond s then
+    if cond s then
       let s ← body s
       pure (.yield s)
     else
diff --git a/hax-lib/proof-libs/lean/Hax/MissingLean/Std/Do/Triple/Basic.lean b/hax-lib/proof-libs/lean/Hax/MissingLean/Std/Do/Triple/Basic.lean
new file mode 100644
index 000000000..11d6e887b
--- /dev/null
+++ b/hax-lib/proof-libs/lean/Hax/MissingLean/Std/Do/Triple/Basic.lean
@@ -0,0 +1,17 @@
+import Std.Do.Triple.Basic
+
+namespace Std.Do
+
+theorem Triple.of_entails_left {m} {ps : PostShape} {β: Type} [Monad m] [WPMonad m ps]
+    (P Q : Assertion ps) (R : PostCond β ps) (x : m β) (hPR : ⦃P⦄ x ⦃R⦄) (hPQ : Q ⊢ₛ P) : ⦃Q⦄ x ⦃R⦄ :=
+  SPred.entails.trans hPQ hPR
+
+theorem Triple.of_entails_right {m} {ps : PostShape} {β: Type} [Monad m] [WPMonad m ps]
+    (P : Assertion ps) (Q R : PostCond β ps) (x : m β) (hPR : ⦃P⦄ x ⦃Q⦄) (hPQ : Q ⊢ₚ R) : ⦃P⦄ x ⦃R⦄ :=
+  SPred.entails.trans hPR (PredTrans.mono _ _ _ hPQ)
+
+theorem Triple.map {m} {ps : PostShape} {α β} [Monad m] [WPMonad m ps] (f : α → β)
+    (x : m α) (P : Assertion ps) (Q : PostCond β ps) :
+    ⦃P⦄ (f <$> x) ⦃Q⦄ ↔ ⦃P⦄ x ⦃(fun a => Q.fst (f a), Q.snd)⦄ := by rw [Triple, WP.map]; rfl
+
+end Std.Do
diff --git a/hax-lib/proof-libs/lean/Hax/MissingLean/Std/Do/Triple/SpecLemmas.lean b/hax-lib/proof-libs/lean/Hax/MissingLean/Std/Do/Triple/SpecLemmas.lean
index 80874ab8c..80696f57c 100644
--- a/hax-lib/proof-libs/lean/Hax/MissingLean/Std/Do/Triple/SpecLemmas.lean
+++ b/hax-lib/proof-libs/lean/Hax/MissingLean/Std/Do/Triple/SpecLemmas.lean
@@ -1,4 +1,5 @@
 import Std.Do.Triple.Basic
+import Hax.MissingLean.Std.Do.Triple.Basic
 import Hax.MissingLean.Init.While
 import Hax.MissingLean.Std.Do.PostCond
 
@@ -11,26 +12,27 @@ theorem Spec.forIn_monoLoopCombinator {m} {ps : PostShape} {β: Type}
     (loop : Loop)
     (init : β)
     (f : Unit → β → m (ForInStep β)) [Loop.MonoLoopCombinator f]
-    (inv : PostCond β ps)
+    (inv : β → Prop)
     (termination : β -> Nat)
+    (post : β → Prop)
     (step : ∀ b,
-      ⦃inv.1 b⦄
+      ⦃⌜ inv b ⌝⦄
         f () b
-      ⦃(fun r => match r with
-        | .yield b' => spred(⌜ termination b' < termination b ⌝ ∧ inv.1 b')
-        | .done b' => inv.1 b', inv.2)⦄) :
-    ⦃inv.1 init⦄ Loop.MonoLoopCombinator.forIn loop init f ⦃(fun b => inv.1 b, inv.2)⦄ := by
+      ⦃⇓ r => match r with
+        | .yield b' => spred(⌜ termination b' < termination b ⌝ ∧ ⌜ inv b' ⌝)
+        | .done b' => ⌜ post b' ⌝⦄) :
+    ⦃⌜ inv init ⌝⦄ Loop.MonoLoopCombinator.forIn loop init f ⦃⇓ b => ⌜ post b ⌝⦄ := by
   unfold Loop.MonoLoopCombinator.forIn Loop.MonoLoopCombinator.forIn.loop Loop.loopCombinator
   apply Triple.bind
   · apply step
   · rintro (b | b)
     · refine Triple.pure b ?_
-      exact SPred.entails.refl (inv.fst b)
+      exact SPred.entails.refl _
     · apply SPred.imp_elim
       apply SPred.pure_elim'
       intro h
       rw [SPred.entails_true_intro]
-      apply Spec.forIn_monoLoopCombinator loop _ f inv termination step
+      apply Spec.forIn_monoLoopCombinator loop _ f inv termination post step
 termination_by termination init
 decreasing_by exact h
 
@@ -40,25 +42,20 @@ theorem Spec.MonoLoopCombinator.while_loop {m} {ps : PostShape} {β: Type}
     [∀ f : Unit → β → m (ForInStep β), Loop.MonoLoopCombinator f]
     (init : β)
     (loop : Loop)
-    (cond: β → m Bool)
+    (cond: β → Bool)
     (body : β → m β)
     (inv: β → Prop)
     (termination : β → Nat)
     (step :
-      ∀ (b : β),
+      ∀ (b : β), cond b →
         ⦃⌜ inv b ⌝⦄
-          do
-            if ← cond b
-            then return ForInStep.yield (← body b)
-            else return ForInStep.done b
-        ⦃(fun r =>
-          match r with
-          | ForInStep.yield b' => spred(⌜ termination b' < termination b ⌝ ∧ ⌜ inv b' ⌝)
-          | ForInStep.done b' => ⌜ inv b' ⌝,
-          ExceptConds.false)⦄ ) :
+          body b
+        ⦃⇓ b' => spred(⌜ termination b' < termination b ⌝ ∧ ⌜ inv b' ⌝)⦄ ) :
     ⦃⌜ inv init ⌝⦄
       Loop.MonoLoopCombinator.while_loop loop cond init body
-    ⦃⇓ b => ⌜ inv b ⌝⦄ := by
+    ⦃⇓ b => ⌜ inv b ∧ ¬ cond b ⌝⦄ := by
   apply Spec.forIn_monoLoopCombinator
-    (inv := (fun b => ⌜ inv b ⌝ , ExceptConds.false))
-    (step := step)
+  intro b
+  by_cases hb : cond b
+  · simpa [hb, Triple.map] using step b hb
+  · simp [hb, Triple.pure]