diff --git a/compiler/rustc_monomorphize/src/mono_checks/mod.rs b/compiler/rustc_monomorphize/src/mono_checks/mod.rs
index 1ecda824fb8c2..459374d860b2c 100644
--- a/compiler/rustc_monomorphize/src/mono_checks/mod.rs
+++ b/compiler/rustc_monomorphize/src/mono_checks/mod.rs
@@ -3,7 +3,7 @@
 //! checks in a way that is friendly to incremental compilation.
 
 use rustc_middle::query::Providers;
-use rustc_middle::ty::{Instance, TyCtxt};
+use rustc_middle::ty::{Instance, InstanceKind, TyCtxt};
 
 mod abi_check;
 mod move_check;
@@ -12,6 +12,11 @@ fn check_mono_item<'tcx>(tcx: TyCtxt<'tcx>, instance: Instance<'tcx>) {
     let body = tcx.instance_mir(instance.def);
     abi_check::check_feature_dependent_abi(tcx, instance, body);
     move_check::check_moves(tcx, instance, body);
+    if let InstanceKind::Item(def_id) = instance.def {
+        if tcx.instantiate_and_check_impossible_predicates((def_id, instance.args)) {
+            tcx.dcx().span_err(tcx.def_span(def_id), "post-mono");
+        }
+    }
 }
 
 pub(super) fn provide(providers: &mut Providers) {
diff --git a/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs b/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs
index 082c356cc5fbd..86b0c1d256f5a 100644
--- a/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs
@@ -870,6 +870,11 @@ where
             continue;
         }
 
+        // Skip RPITITs, since the AFIDT feature means that they are always implied.
+        if cx.is_impl_trait_in_trait(associated_type_def_id) {
+            continue;
+        }
+
         requirements
             .extend(cx.item_bounds(associated_type_def_id).iter_instantiated(cx, trait_ref.args));
     }
diff --git a/compiler/rustc_trait_selection/src/traits/mod.rs b/compiler/rustc_trait_selection/src/traits/mod.rs
index 105cb9175717d..fa9fbb558e9c0 100644
--- a/compiler/rustc_trait_selection/src/traits/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/mod.rs
@@ -703,8 +703,11 @@ fn replace_param_and_infer_args_with_placeholder<'tcx>(
 /// used during analysis.
 pub fn impossible_predicates<'tcx>(tcx: TyCtxt<'tcx>, predicates: Vec<ty::Clause<'tcx>>) -> bool {
     debug!("impossible_predicates(predicates={:?})", predicates);
-    let (infcx, param_env) =
-        tcx.infer_ctxt().build_with_typing_env(ty::TypingEnv::fully_monomorphized());
+    let (infcx, param_env) = tcx
+        .infer_ctxt()
+        .with_next_trait_solver(true)
+        .build_with_typing_env(ty::TypingEnv::fully_monomorphized());
+
     let ocx = ObligationCtxt::new(&infcx);
     let predicates = ocx.normalize(&ObligationCause::dummy(), param_env, predicates);
     for predicate in predicates {
@@ -717,13 +720,6 @@ pub fn impossible_predicates<'tcx>(tcx: TyCtxt<'tcx>, predicates: Vec<ty::Clause
         return true;
     }
 
-    // Leak check for any higher-ranked trait mismatches.
-    // We only need to do this in the old solver, since the new solver already
-    // leak-checks.
-    if !infcx.next_trait_solver() && infcx.leak_check(ty::UniverseIndex::ROOT, None).is_err() {
-        return true;
-    }
-
     false
 }