diff --git a/cargo-marker/src/driver.rs b/cargo-marker/src/driver.rs
index be66cace..da34d002 100644
--- a/cargo-marker/src/driver.rs
+++ b/cargo-marker/src/driver.rs
@@ -41,7 +41,7 @@ pub fn print_driver_version() {
 }
 
 /// This tries to install the rustc driver specified in [`DEFAULT_DRIVER_INFO`].
-pub fn install_driver(verbose: bool) -> Result<(), ExitStatus> {
+pub fn install_driver(verbose: bool, dev_build: bool) -> Result<(), ExitStatus> {
     // The toolchain, driver version and api version should ideally be configurable.
     // However, that will require more prototyping and has a low priority rn.
     // See #60
@@ -50,12 +50,7 @@ pub fn install_driver(verbose: bool) -> Result<(), ExitStatus> {
     let toolchain = &DEFAULT_DRIVER_INFO.toolchain;
     check_toolchain(toolchain)?;
 
-    build_driver(
-        toolchain,
-        &DEFAULT_DRIVER_INFO.version,
-        verbose,
-        cfg!(feature = "dev-build"),
-    )?;
+    build_driver(toolchain, &DEFAULT_DRIVER_INFO.version, verbose, dev_build)?;
 
     // We don't want to advice the user, to install the driver again.
     check_driver(verbose, false)
diff --git a/cargo-marker/src/main.rs b/cargo-marker/src/main.rs
index 51db32f5..0a38c02c 100644
--- a/cargo-marker/src/main.rs
+++ b/cargo-marker/src/main.rs
@@ -78,6 +78,7 @@ fn main() -> Result<(), ExitStatus> {
     );
 
     let verbose = matches.get_flag("verbose");
+    let dev_build = cfg!(feature = "dev-build");
 
     if matches.get_flag("version") {
         print_version(verbose);
@@ -85,14 +86,19 @@ fn main() -> Result<(), ExitStatus> {
     }
 
     match matches.subcommand() {
-        Some(("setup", _args)) => driver::install_driver(verbose),
-        Some(("check", args)) => run_check(args, verbose),
-        None => run_check(&matches, verbose),
+        Some(("setup", _args)) => driver::install_driver(verbose, dev_build),
+        Some(("check", args)) => run_check(args, verbose, dev_build),
+        None => run_check(&matches, verbose, dev_build),
         _ => unreachable!(),
     }
 }
 
-fn run_check(matches: &clap::ArgMatches, verbose: bool) -> Result<(), ExitStatus> {
+fn run_check(matches: &clap::ArgMatches, verbose: bool, dev_build: bool) -> Result<(), ExitStatus> {
+    // If this is a dev build, we want to recompile the driver before checking
+    if dev_build {
+        driver::install_driver(verbose, dev_build)?;
+    }
+
     let mut lint_crates = vec![];
     if let Some(cmd_lint_crates) = matches.get_many::<OsString>("lints") {
         println!();
diff --git a/marker_driver_rustc/src/conversion/generic.rs b/marker_driver_rustc/src/conversion/generic.rs
index 96611b2c..e1b54a8d 100644
--- a/marker_driver_rustc/src/conversion/generic.rs
+++ b/marker_driver_rustc/src/conversion/generic.rs
@@ -2,13 +2,42 @@ use marker_api::ast::{
     generic::{BindingGenericArg, GenericArgKind, GenericArgs, Lifetime, LifetimeKind, TraitBound, TyParamBound},
     TraitRef,
 };
+use rustc_hir as hir;
 
 use crate::context::RustcContext;
 
 use super::{to_generic_id, to_item_id, to_span_id, to_symbol_id, ty::TyConverter};
 
-pub fn to_api_lifetime<'ast>(
-    _cx: &'ast RustcContext<'ast, '_>,
+pub fn conv_ast_bound<'ast, 'tcx>(
+    cx: &'ast RustcContext<'ast, 'tcx>,
+    bounds: &'tcx [hir::GenericBound],
+) -> &'ast [TyParamBound<'ast>] {
+    if bounds.is_empty() {
+        return &[];
+    }
+
+    let bounds: Vec<_> = bounds
+        .iter()
+        .filter_map(|bound| match bound {
+            hir::GenericBound::Trait(trait_ref, modifier) => Some(TyParamBound::TraitBound(cx.storage.alloc(|| {
+                TraitBound::new(
+                    !matches!(modifier, hir::TraitBoundModifier::None),
+                    to_api_trait_ref(cx, &trait_ref.trait_ref),
+                    to_span_id(bound.span()),
+                )
+            }))),
+            hir::GenericBound::LangItemTrait(_, _, _, _) => todo!(),
+            hir::GenericBound::Outlives(rust_lt) => {
+                to_api_lifetime(cx, rust_lt).map(|api_lt| TyParamBound::Lifetime(cx.storage.alloc(|| api_lt)))
+            },
+        })
+        .collect();
+
+    cx.storage.alloc_slice_iter(bounds.into_iter())
+}
+
+pub fn to_api_lifetime<'ast, 'tcx>(
+    _cx: &'ast RustcContext<'ast, 'tcx>,
     rust_lt: &rustc_hir::Lifetime,
 ) -> Option<Lifetime<'ast>> {
     let kind = match rust_lt.res {
diff --git a/marker_driver_rustc/src/conversion/item.rs b/marker_driver_rustc/src/conversion/item.rs
index 35d0f839..48f2e8fb 100644
--- a/marker_driver_rustc/src/conversion/item.rs
+++ b/marker_driver_rustc/src/conversion/item.rs
@@ -1,8 +1,5 @@
 use marker_api::ast::{
-    generic::{
-        GenericParamKind, GenericParams, LifetimeClause, LifetimeParam, TraitBound, TyClause, TyParam, TyParamBound,
-        WhereClauseKind,
-    },
+    generic::{GenericParamKind, GenericParams, LifetimeClause, LifetimeParam, TyClause, TyParam, WhereClauseKind},
     item::{
         AdtKind, AssocItemKind, CommonItemData, ConstItem, EnumItem, EnumVariant, ExternBlockItem, ExternCrateItem,
         ExternItemKind, Field, FnItem, ImplItem, ItemKind, ModItem, StaticItem, StructItem, TraitItem, TyAliasItem,
@@ -16,7 +13,7 @@ use rustc_hir as hir;
 use crate::context::RustcContext;
 
 use super::{
-    generic::{to_api_lifetime, to_api_trait_ref},
+    generic::{conv_ast_bound, to_api_lifetime, to_api_trait_ref},
     to_api_abi, to_api_body_id, to_api_path, to_generic_id, to_item_id, to_rustc_item_id, to_span_id, to_symbol_id,
     ty::TyConverter,
 };
@@ -115,7 +112,7 @@ impl<'ast, 'tcx> ItemConverter<'ast, 'tcx> {
                     data,
                     matches!(unsafety, hir::Unsafety::Unsafe),
                     self.conv_generic(generics),
-                    self.conv_generic_bounds(bounds),
+                    conv_ast_bound(self.cx, bounds),
                     self.conv_trait_items(items),
                 )
             })),
@@ -219,7 +216,7 @@ impl<'ast, 'tcx> ItemConverter<'ast, 'tcx> {
                 TyAliasItem::new(
                     data,
                     self.conv_generic(trait_item.generics),
-                    self.conv_generic_bounds(bounds),
+                    conv_ast_bound(self.cx, bounds),
                     ty.map(|ty| self.conv_ty(ty)),
                 )
             })),
@@ -310,31 +307,6 @@ impl<'ast, 'tcx> ItemConverter<'ast, 'tcx> {
         self.cx.storage.alloc_slice_iter(params.into_iter())
     }
 
-    fn conv_generic_bounds(&self, bounds: hir::GenericBounds<'tcx>) -> &'ast [TyParamBound<'ast>] {
-        if bounds.is_empty() {
-            return &[];
-        }
-
-        let bounds: Vec<_> = bounds
-            .iter()
-            .filter_map(|bound| match bound {
-                hir::GenericBound::Trait(trait_ref, modifier) => Some(TyParamBound::TraitBound(self.alloc(|| {
-                    TraitBound::new(
-                        !matches!(modifier, hir::TraitBoundModifier::None),
-                        to_api_trait_ref(self.cx, &trait_ref.trait_ref),
-                        to_span_id(bound.span()),
-                    )
-                }))),
-                hir::GenericBound::LangItemTrait(_, _, _, _) => todo!(),
-                hir::GenericBound::Outlives(rust_lt) => {
-                    to_api_lifetime(self.cx, rust_lt).map(|api_lt| TyParamBound::Lifetime(self.alloc(|| api_lt)))
-                },
-            })
-            .collect();
-
-        self.cx.storage.alloc_slice_iter(bounds.into_iter())
-    }
-
     fn conv_generic(&self, rustc_generics: &hir::Generics<'tcx>) -> GenericParams<'ast> {
         // FIXME: Update implementation to store the parameter bounds in the parameters
         let clauses: Vec<_> = rustc_generics
@@ -348,7 +320,7 @@ impl<'ast, 'tcx> ItemConverter<'ast, 'tcx> {
                         let params = GenericParams::new(self.conv_generic_params(ty_bound.bound_generic_params), &[]);
                         let ty = self.conv_ty(ty_bound.bounded_ty);
                         Some(WhereClauseKind::Ty(self.alloc(|| {
-                            TyClause::new(Some(params), ty, self.conv_generic_bounds(predicate.bounds()))
+                            TyClause::new(Some(params), ty, conv_ast_bound(self.cx, predicate.bounds()))
                         })))
                     },
                     hir::WherePredicate::RegionPredicate(lifetime_bound) => {
diff --git a/marker_driver_rustc/src/conversion/ty.rs b/marker_driver_rustc/src/conversion/ty.rs
index 9f748f75..2fbfdc6d 100644
--- a/marker_driver_rustc/src/conversion/ty.rs
+++ b/marker_driver_rustc/src/conversion/ty.rs
@@ -1,7 +1,8 @@
 use marker_api::ast::{
     ty::{
-        AliasTy, ArrayTy, BoolTy, CommonTyData, EnumTy, FnTy, GenericTy, InferredTy, NeverTy, NumKind, NumTy, RawPtrTy,
-        RefTy, RelativeTy, SelfTy, SliceTy, StructTy, TextKind, TextTy, TraitObjTy, TupleTy, TyKind, UnionTy,
+        AliasTy, ArrayTy, BoolTy, CommonTyData, EnumTy, FnTy, GenericTy, ImplTraitTy, InferredTy, NeverTy, NumKind,
+        NumTy, RawPtrTy, RefTy, RelativeTy, SelfTy, SliceTy, StructTy, TextKind, TextTy, TraitObjTy, TupleTy, TyKind,
+        UnionTy,
     },
     CommonCallableData, Parameter,
 };
@@ -12,7 +13,7 @@ use crate::{
 };
 
 use super::{
-    generic::{to_api_generic_args, to_api_lifetime, to_api_trait_bounds_from_hir},
+    generic::{conv_ast_bound, to_api_generic_args, to_api_lifetime, to_api_trait_bounds_from_hir},
     to_generic_id, to_item_id, to_span_id, to_ty_def_id,
 };
 
@@ -82,10 +83,15 @@ impl<'ast, 'tcx> TyConverter<'ast, 'tcx> {
                 TyKind::Tuple(self.cx.storage.alloc(|| TupleTy::new(data, api_tys)))
             },
             hir::TyKind::Path(qpath) => self.conv_syn_qpath(data, qpath),
-            hir::TyKind::OpaqueDef(_, _, _) => {
-                // This requires function items to be implemented. Therefore we'll leave this as an open TODO for
-                // now
-                todo!("{:#?}", rustc_ty)
+            hir::TyKind::OpaqueDef(id, _, _) => {
+                // `impl Trait` in rustc are implemented as Items with the kind `OpaqueTy`
+                let item = self.cx.rustc_cx.hir().item(*id);
+                let hir::ItemKind::OpaqueTy(opty) = &item.kind else {
+                    unreachable!("the item of a `OpaqueDef` should be `OpaqueTy` {item:#?}");
+                };
+                let rust_bound = conv_ast_bound(self.cx, opty.bounds);
+                // FIXME: Generics are a bit weird with opaque types
+                TyKind::ImplTrait(self.cx.storage.alloc(|| ImplTraitTy::new(data, rust_bound)))
             },
             hir::TyKind::TraitObject(rust_bounds, rust_lt, _syntax) => TyKind::TraitObj(
                 self.cx