diff --git a/stainless_data/src/ast.rs b/stainless_data/src/ast.rs
index 6648ce93..12dc986e 100644
--- a/stainless_data/src/ast.rs
+++ b/stainless_data/src/ast.rs
@@ -149,6 +149,21 @@ impl<'l, 'a> From<&'l ValDef<'a>> for &'l Variable<'a> {
   }
 }
 
+impl Variable<'_> {
+  pub fn is_mutable(&self) -> bool {
+    self.flags.iter().any(|f| match f {
+      Flag::IsVar(_) => true,
+      _ => false,
+    })
+  }
+}
+
+impl ValDef<'_> {
+  pub fn is_mutable(&self) -> bool {
+    self.v.is_mutable()
+  }
+}
+
 // Additional helpers that mirror those in Inox
 
 pub fn Int32Literal(value: Int) -> BVLiteral {
diff --git a/stainless_extraction/src/bindings.rs b/stainless_extraction/src/bindings.rs
index 9c8ca01b..0771d984 100644
--- a/stainless_extraction/src/bindings.rs
+++ b/stainless_extraction/src/bindings.rs
@@ -20,7 +20,7 @@ impl<'a, 'l, 'tcx> BodyExtractor<'a, 'l, 'tcx> {
         .pat
         .simple_ident()
         .and_then(|ident| flags_by_symbol.remove(&ident.name));
-      let (var, _) = self.extract_binding(param.pat.hir_id, flags);
+      let var = self.extract_binding(param.pat.hir_id, flags);
       self.dcx.add_param(self.factory().ValDef(var));
     }
 
@@ -35,11 +35,7 @@ impl<'a, 'l, 'tcx> BodyExtractor<'a, 'l, 'tcx> {
 
   /// Extract a binding based on the binding node's HIR id.
   /// Updates `dcx` if the binding hadn't been extracted before.
-  fn extract_binding(
-    &mut self,
-    hir_id: HirId,
-    flags: Option<Flags>,
-  ) -> (&'l st::Variable<'l>, bool) {
+  fn extract_binding(&mut self, hir_id: HirId, flags_opt: Option<Flags>) -> &'l st::Variable<'l> {
     self.dcx.get_var(hir_id).unwrap_or_else(|| {
       let xtor = &mut self.base;
 
@@ -85,13 +81,18 @@ impl<'a, 'l, 'tcx> BodyExtractor<'a, 'l, 'tcx> {
       };
 
       // Build a Variable node
+      let f = xtor.factory();
       let tpe = xtor.extract_ty(self.tables.node_type(hir_id), &self.txtcx, span);
-      let flags = flags
-        .map(|flags| flags.to_stainless(xtor.factory()))
-        .unwrap_or_default();
-      let var = xtor.factory().Variable(id, tpe, flags);
-      self.dcx.add_var(hir_id, var, mutable);
-      (var, mutable)
+      let flags = flags_opt
+        .map(|flags| flags.to_stainless(f))
+        .into_iter()
+        .flatten()
+        // Add @var flag if the param is mutable
+        .chain(mutable.then(|| f.IsVar().into()))
+        .collect();
+      let var = f.Variable(id, tpe, flags);
+      self.dcx.add_var(hir_id, var);
+      var
     })
   }
 }
@@ -99,7 +100,7 @@ impl<'a, 'l, 'tcx> BodyExtractor<'a, 'l, 'tcx> {
 /// DefContext tracks available bindings
 #[derive(Clone, Debug)]
 pub(super) struct DefContext<'l> {
-  vars: HashMap<HirId, (&'l st::Variable<'l>, bool)>,
+  vars: HashMap<HirId, &'l st::Variable<'l>>,
   params: Vec<&'l st::ValDef<'l>>,
 }
 
@@ -115,14 +116,9 @@ impl<'l> DefContext<'l> {
     &self.params[..]
   }
 
-  pub(super) fn add_var(
-    &mut self,
-    hir_id: HirId,
-    var: &'l st::Variable<'l>,
-    mutable: bool,
-  ) -> &mut Self {
+  pub(super) fn add_var(&mut self, hir_id: HirId, var: &'l st::Variable<'l>) -> &mut Self {
     assert!(!self.vars.contains_key(&hir_id));
-    self.vars.insert(hir_id, (var, mutable));
+    self.vars.insert(hir_id, var);
     self
   }
 
@@ -133,7 +129,7 @@ impl<'l> DefContext<'l> {
   }
 
   #[inline]
-  pub(super) fn get_var(&self, hir_id: HirId) -> Option<(&'l st::Variable<'l>, bool)> {
+  pub(super) fn get_var(&self, hir_id: HirId) -> Option<&'l st::Variable<'l>> {
     self.vars.get(&hir_id).copied()
   }
 }
diff --git a/stainless_extraction/src/expr.rs b/stainless_extraction/src/expr.rs
index 9dd80de4..18f43f36 100644
--- a/stainless_extraction/src/expr.rs
+++ b/stainless_extraction/src/expr.rs
@@ -31,7 +31,7 @@ impl<'a, 'l, 'tcx> BodyExtractor<'a, 'l, 'tcx> {
       ExprKind::LogicalOp { .. } => self.extract_logical_op(expr),
       ExprKind::Tuple { .. } => self.extract_tuple(expr),
       ExprKind::Field { lhs, name } => self.extract_field(lhs, name),
-      ExprKind::VarRef { id } => self.fetch_var(id).0.into(),
+      ExprKind::VarRef { id } => self.fetch_var(id).into(),
       ExprKind::Call { ty, ref args, .. } => self.extract_call_like(ty, args, expr.span),
       ExprKind::Adt { .. } => self.extract_adt_construction(expr),
       ExprKind::Block { body: ast_block } => {
@@ -619,7 +619,7 @@ impl<'a, 'l, 'tcx> BodyExtractor<'a, 'l, 'tcx> {
       box kind @ PatKind::Binding { .. } => {
         assert!(binder.is_none());
         match self.try_pattern_to_var(&kind, true) {
-          Ok((binder, _)) => match kind {
+          Ok(binder) => match kind {
             PatKind::Binding {
               subpattern: Some(subpattern),
               ..
@@ -716,10 +716,7 @@ impl<'a, 'l, 'tcx> BodyExtractor<'a, 'l, 'tcx> {
     let lhs = self.mirror(lhs);
     let lhs = self.strip_scope(lhs);
     match lhs.kind {
-      ExprKind::VarRef { id } => self
-        .factory()
-        .Assignment(self.fetch_var(id).0, value)
-        .into(),
+      ExprKind::VarRef { id } => self.factory().Assignment(self.fetch_var(id), value).into(),
 
       ExprKind::Field { lhs, name } => {
         let lhs = self.mirror(lhs);
@@ -827,14 +824,14 @@ impl<'a, 'l, 'tcx> BodyExtractor<'a, 'l, 'tcx> {
                 &format!("Cannot extract complex pattern in let: {}", reason),
                 pattern.span,
               ),
-              Ok((vd, mutable)) => {
+              Ok(vd) => {
                 // recurse the extract all the following statements
                 let exprs = acc_exprs.clone();
                 acc_exprs.clear();
                 let body_expr = self.extract_block_(stmts, acc_exprs, acc_specs, final_expr);
                 // wrap that body expression into the Let
                 let init = self.extract_expr_ref(init);
-                let last_expr = if mutable {
+                let last_expr = if vd.is_mutable() {
                   f.LetVar(vd, init, body_expr).into()
                 } else {
                   f.Let(vd, init, body_expr).into()
@@ -902,7 +899,7 @@ impl<'a, 'l, 'tcx> BodyExtractor<'a, 'l, 'tcx> {
     &self,
     pat_kind: &PatKind<'tcx>,
     allow_subpattern: bool,
-  ) -> Result<(&'l st::ValDef<'l>, bool)> {
+  ) -> Result<&'l st::ValDef<'l>> {
     match pat_kind {
       PatKind::Binding {
         subpattern: Some(_),
@@ -921,9 +918,9 @@ impl<'a, 'l, 'tcx> BodyExtractor<'a, 'l, 'tcx> {
         var: hir_id,
         ..
       } => {
-        let (var, mutable) = self.fetch_var(*hir_id);
-        if *mutability == Mutability::Not || mutable {
-          Ok((self.factory().ValDef(var), mutable))
+        let var = self.fetch_var(*hir_id);
+        if *mutability == Mutability::Not || var.is_mutable() {
+          Ok(self.factory().ValDef(var))
         } else {
           Err("Binding mode not allowed")
         }
diff --git a/stainless_extraction/src/lib.rs b/stainless_extraction/src/lib.rs
index 74be9849..bec8f0ac 100644
--- a/stainless_extraction/src/lib.rs
+++ b/stainless_extraction/src/lib.rs
@@ -1,5 +1,6 @@
 #![feature(rustc_private)]
 #![feature(box_patterns)]
+#![feature(bool_to_option)]
 
 #[macro_use]
 extern crate lazy_static;
@@ -372,7 +373,7 @@ impl<'a, 'l, 'tcx> BodyExtractor<'a, 'l, 'tcx> {
     self.base.factory()
   }
 
-  fn fetch_var(&self, hir_id: HirId) -> (&'l st::Variable<'l>, bool) {
+  fn fetch_var(&self, hir_id: HirId) -> &'l st::Variable<'l> {
     let span: Span = self.tcx().hir().span(hir_id);
     self
       .dcx
diff --git a/stainless_extraction/src/spec.rs b/stainless_extraction/src/spec.rs
index 52937504..3f135683 100644
--- a/stainless_extraction/src/spec.rs
+++ b/stainless_extraction/src/spec.rs
@@ -106,13 +106,13 @@ impl<'a, 'l, 'tcx> BodyExtractor<'a, 'l, 'tcx> {
           .expect("No return parameter on post spec function");
 
         // Preregister the ret binding with the return_id
-        bxtor.dcx.add_var(return_param_id, return_var, false);
+        bxtor.dcx.add_var(return_param_id, return_var);
       }
 
       // Register all other bindings
       assert_eq!(outer_fn_params.len(), spec_param_ids.len());
       for (vd, sid) in outer_fn_params.iter().zip(spec_param_ids) {
-        bxtor.dcx.add_var(sid, vd.v, false);
+        bxtor.dcx.add_var(sid, vd.v);
       }
       // Pick up any additional local bindings
       // (A spec neither has flags on the params, nor additional evidence params)