diff --git a/compiler/rustc_hir_analysis/src/check/dropck.rs b/compiler/rustc_hir_analysis/src/check/dropck.rs
index 2bb724138f5..111bf5e5455 100644
--- a/compiler/rustc_hir_analysis/src/check/dropck.rs
+++ b/compiler/rustc_hir_analysis/src/check/dropck.rs
@@ -253,10 +253,6 @@ fn tcx(&self) -> TyCtxt<'tcx> {
         self.tcx
     }
 
-    fn intercrate(&self) -> bool {
-        false
-    }
-
     fn param_env(&self) -> ty::ParamEnv<'tcx> {
         self.param_env
     }
@@ -269,10 +265,6 @@ fn a_is_expected(&self) -> bool {
         true
     }
 
-    fn mark_ambiguous(&mut self) {
-        bug!()
-    }
-
     fn relate_with_variance<T: Relate<'tcx>>(
         &mut self,
         _: ty::Variance,
diff --git a/compiler/rustc_infer/src/infer/combine.rs b/compiler/rustc_infer/src/infer/combine.rs
index 88a28e26005..fe45b5ebe61 100644
--- a/compiler/rustc_infer/src/infer/combine.rs
+++ b/compiler/rustc_infer/src/infer/combine.rs
@@ -137,6 +137,18 @@ pub fn super_combine_tys<R>(
                 Err(TypeError::Sorts(ty::relate::expected_found(relation, a, b)))
             }
 
+            // During coherence, opaque types should be treated as *possibly*
+            // equal to each other, even if their generic params differ, as
+            // they could resolve to the same hidden type, even for different
+            // generic params.
+            (
+                &ty::Alias(ty::Opaque, ty::AliasTy { def_id: a_def_id, .. }),
+                &ty::Alias(ty::Opaque, ty::AliasTy { def_id: b_def_id, .. }),
+            ) if self.intercrate && a_def_id == b_def_id => {
+                relation.register_predicates([ty::Binder::dummy(ty::PredicateKind::Ambiguous)]);
+                Ok(a)
+            }
+
             _ => ty::relate::super_relate_tys(relation, a, b),
         }
     }
@@ -505,10 +517,6 @@ pub fn register_predicates(&mut self, obligations: impl IntoIterator<Item: ToPre
             Obligation::new(self.infcx.tcx, self.trace.cause.clone(), self.param_env, to_pred)
         }))
     }
-
-    pub fn mark_ambiguous(&mut self) {
-        self.register_predicates([ty::Binder::dummy(ty::PredicateKind::Ambiguous)]);
-    }
 }
 
 struct Generalizer<'cx, 'tcx> {
@@ -581,10 +589,6 @@ fn tcx(&self) -> TyCtxt<'tcx> {
         self.infcx.tcx
     }
 
-    fn intercrate(&self) -> bool {
-        self.infcx.intercrate
-    }
-
     fn param_env(&self) -> ty::ParamEnv<'tcx> {
         self.param_env
     }
@@ -597,10 +601,6 @@ fn a_is_expected(&self) -> bool {
         true
     }
 
-    fn mark_ambiguous(&mut self) {
-        span_bug!(self.cause.span, "opaque types are handled in `tys`");
-    }
-
     fn binders<T>(
         &mut self,
         a: ty::Binder<'tcx, T>,
diff --git a/compiler/rustc_infer/src/infer/equate.rs b/compiler/rustc_infer/src/infer/equate.rs
index 38002357cde..fe4a2dd3800 100644
--- a/compiler/rustc_infer/src/infer/equate.rs
+++ b/compiler/rustc_infer/src/infer/equate.rs
@@ -35,10 +35,6 @@ fn tcx(&self) -> TyCtxt<'tcx> {
         self.fields.tcx()
     }
 
-    fn intercrate(&self) -> bool {
-        self.fields.infcx.intercrate
-    }
-
     fn param_env(&self) -> ty::ParamEnv<'tcx> {
         self.fields.param_env
     }
@@ -47,10 +43,6 @@ fn a_is_expected(&self) -> bool {
         self.a_is_expected
     }
 
-    fn mark_ambiguous(&mut self) {
-        self.fields.mark_ambiguous();
-    }
-
     fn relate_item_substs(
         &mut self,
         _item_def_id: DefId,
diff --git a/compiler/rustc_infer/src/infer/error_reporting/mod.rs b/compiler/rustc_infer/src/infer/error_reporting/mod.rs
index d53e64830ff..c9956b60a56 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/mod.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/mod.rs
@@ -2697,11 +2697,6 @@ fn tcx(&self) -> TyCtxt<'tcx> {
         self.0.tcx
     }
 
-    fn intercrate(&self) -> bool {
-        assert!(!self.0.intercrate);
-        false
-    }
-
     fn param_env(&self) -> ty::ParamEnv<'tcx> {
         // Unused, only for consts which we treat as always equal
         ty::ParamEnv::empty()
@@ -2715,10 +2710,6 @@ fn a_is_expected(&self) -> bool {
         true
     }
 
-    fn mark_ambiguous(&mut self) {
-        bug!()
-    }
-
     fn relate_with_variance<T: relate::Relate<'tcx>>(
         &mut self,
         _variance: ty::Variance,
diff --git a/compiler/rustc_infer/src/infer/glb.rs b/compiler/rustc_infer/src/infer/glb.rs
index 6395c4d4b20..2f659d9a665 100644
--- a/compiler/rustc_infer/src/infer/glb.rs
+++ b/compiler/rustc_infer/src/infer/glb.rs
@@ -29,11 +29,6 @@ fn tag(&self) -> &'static str {
         "Glb"
     }
 
-    fn intercrate(&self) -> bool {
-        assert!(!self.fields.infcx.intercrate);
-        false
-    }
-
     fn tcx(&self) -> TyCtxt<'tcx> {
         self.fields.tcx()
     }
@@ -46,10 +41,6 @@ fn a_is_expected(&self) -> bool {
         self.a_is_expected
     }
 
-    fn mark_ambiguous(&mut self) {
-        bug!("mark_ambiguous used outside of coherence");
-    }
-
     fn relate_with_variance<T: Relate<'tcx>>(
         &mut self,
         variance: ty::Variance,
diff --git a/compiler/rustc_infer/src/infer/lub.rs b/compiler/rustc_infer/src/infer/lub.rs
index 98cbd4c561c..e41ec7e6c01 100644
--- a/compiler/rustc_infer/src/infer/lub.rs
+++ b/compiler/rustc_infer/src/infer/lub.rs
@@ -29,11 +29,6 @@ fn tag(&self) -> &'static str {
         "Lub"
     }
 
-    fn intercrate(&self) -> bool {
-        assert!(!self.fields.infcx.intercrate);
-        false
-    }
-
     fn tcx(&self) -> TyCtxt<'tcx> {
         self.fields.tcx()
     }
@@ -46,10 +41,6 @@ fn a_is_expected(&self) -> bool {
         self.a_is_expected
     }
 
-    fn mark_ambiguous(&mut self) {
-        bug!("mark_ambiguous used outside of coherence");
-    }
-
     fn relate_with_variance<T: Relate<'tcx>>(
         &mut self,
         variance: ty::Variance,
diff --git a/compiler/rustc_infer/src/infer/nll_relate/mod.rs b/compiler/rustc_infer/src/infer/nll_relate/mod.rs
index f5d20cb7ebf..7616a996da1 100644
--- a/compiler/rustc_infer/src/infer/nll_relate/mod.rs
+++ b/compiler/rustc_infer/src/infer/nll_relate/mod.rs
@@ -443,10 +443,6 @@ fn tcx(&self) -> TyCtxt<'tcx> {
         self.infcx.tcx
     }
 
-    fn intercrate(&self) -> bool {
-        self.infcx.intercrate
-    }
-
     fn param_env(&self) -> ty::ParamEnv<'tcx> {
         self.delegate.param_env()
     }
@@ -459,17 +455,6 @@ fn a_is_expected(&self) -> bool {
         true
     }
 
-    fn mark_ambiguous(&mut self) {
-        let cause = ObligationCause::dummy_with_span(self.delegate.span());
-        let param_env = self.delegate.param_env();
-        self.delegate.register_obligations(vec![Obligation::new(
-            self.tcx(),
-            cause,
-            param_env,
-            ty::Binder::dummy(ty::PredicateKind::Ambiguous),
-        )]);
-    }
-
     #[instrument(skip(self, info), level = "trace", ret)]
     fn relate_with_variance<T: Relate<'tcx>>(
         &mut self,
@@ -834,11 +819,6 @@ fn tcx(&self) -> TyCtxt<'tcx> {
         self.infcx.tcx
     }
 
-    fn intercrate(&self) -> bool {
-        assert!(!self.infcx.intercrate);
-        false
-    }
-
     fn param_env(&self) -> ty::ParamEnv<'tcx> {
         self.delegate.param_env()
     }
@@ -851,10 +831,6 @@ fn a_is_expected(&self) -> bool {
         true
     }
 
-    fn mark_ambiguous(&mut self) {
-        bug!()
-    }
-
     fn relate_with_variance<T: Relate<'tcx>>(
         &mut self,
         variance: ty::Variance,
diff --git a/compiler/rustc_infer/src/infer/outlives/test_type_match.rs b/compiler/rustc_infer/src/infer/outlives/test_type_match.rs
index 3c6cc2b9001..01f900f050e 100644
--- a/compiler/rustc_infer/src/infer/outlives/test_type_match.rs
+++ b/compiler/rustc_infer/src/infer/outlives/test_type_match.rs
@@ -137,10 +137,6 @@ fn tag(&self) -> &'static str {
         "Match"
     }
 
-    fn intercrate(&self) -> bool {
-        false
-    }
-
     fn tcx(&self) -> TyCtxt<'tcx> {
         self.tcx
     }
@@ -151,10 +147,6 @@ fn a_is_expected(&self) -> bool {
         true
     } // irrelevant
 
-    fn mark_ambiguous(&mut self) {
-        bug!()
-    }
-
     #[instrument(level = "trace", skip(self))]
     fn relate_with_variance<T: Relate<'tcx>>(
         &mut self,
diff --git a/compiler/rustc_infer/src/infer/sub.rs b/compiler/rustc_infer/src/infer/sub.rs
index fc73ca7606d..0dd73a6e999 100644
--- a/compiler/rustc_infer/src/infer/sub.rs
+++ b/compiler/rustc_infer/src/infer/sub.rs
@@ -35,10 +35,6 @@ fn tag(&self) -> &'static str {
         "Sub"
     }
 
-    fn intercrate(&self) -> bool {
-        self.fields.infcx.intercrate
-    }
-
     fn tcx(&self) -> TyCtxt<'tcx> {
         self.fields.infcx.tcx
     }
@@ -51,10 +47,6 @@ fn a_is_expected(&self) -> bool {
         self.a_is_expected
     }
 
-    fn mark_ambiguous(&mut self) {
-        self.fields.mark_ambiguous()
-    }
-
     fn with_cause<F, R>(&mut self, cause: Cause, f: F) -> R
     where
         F: FnOnce(&mut Self) -> R,
diff --git a/compiler/rustc_middle/src/ty/_match.rs b/compiler/rustc_middle/src/ty/_match.rs
index df9aa765dc1..468c2c818b2 100644
--- a/compiler/rustc_middle/src/ty/_match.rs
+++ b/compiler/rustc_middle/src/ty/_match.rs
@@ -37,10 +37,6 @@ fn tcx(&self) -> TyCtxt<'tcx> {
         self.tcx
     }
 
-    fn intercrate(&self) -> bool {
-        false
-    }
-
     fn param_env(&self) -> ty::ParamEnv<'tcx> {
         self.param_env
     }
@@ -48,10 +44,6 @@ fn a_is_expected(&self) -> bool {
         true
     } // irrelevant
 
-    fn mark_ambiguous(&mut self) {
-        bug!()
-    }
-
     fn relate_with_variance<T: Relate<'tcx>>(
         &mut self,
         _: ty::Variance,
diff --git a/compiler/rustc_middle/src/ty/relate.rs b/compiler/rustc_middle/src/ty/relate.rs
index 3fc5f5bed8f..46c931d61dc 100644
--- a/compiler/rustc_middle/src/ty/relate.rs
+++ b/compiler/rustc_middle/src/ty/relate.rs
@@ -22,8 +22,6 @@ pub enum Cause {
 pub trait TypeRelation<'tcx>: Sized {
     fn tcx(&self) -> TyCtxt<'tcx>;
 
-    fn intercrate(&self) -> bool;
-
     fn param_env(&self) -> ty::ParamEnv<'tcx>;
 
     /// Returns a static string we can use for printouts.
@@ -33,9 +31,6 @@ pub trait TypeRelation<'tcx>: Sized {
     /// relation. Just affects error messages.
     fn a_is_expected(&self) -> bool;
 
-    /// Used during coherence. If called, must emit an always-ambiguous obligation.
-    fn mark_ambiguous(&mut self);
-
     fn with_cause<F, R>(&mut self, _cause: Cause, f: F) -> R
     where
         F: FnOnce(&mut Self) -> R,
@@ -559,23 +554,16 @@ pub fn super_relate_tys<'tcx, R: TypeRelation<'tcx>>(
             &ty::Alias(ty::Opaque, ty::AliasTy { def_id: a_def_id, substs: a_substs, .. }),
             &ty::Alias(ty::Opaque, ty::AliasTy { def_id: b_def_id, substs: b_substs, .. }),
         ) if a_def_id == b_def_id => {
-            if relation.intercrate() {
-                // During coherence, opaque types should be treated as equal to each other, even if their generic params
-                // differ, as they could resolve to the same hidden type, even for different generic params.
-                relation.mark_ambiguous();
-                Ok(a)
-            } else {
-                let opt_variances = tcx.variances_of(a_def_id);
-                let substs = relate_substs_with_variances(
-                    relation,
-                    a_def_id,
-                    opt_variances,
-                    a_substs,
-                    b_substs,
-                    false, // do not fetch `type_of(a_def_id)`, as it will cause a cycle
-                )?;
-                Ok(tcx.mk_opaque(a_def_id, substs))
-            }
+            let opt_variances = tcx.variances_of(a_def_id);
+            let substs = relate_substs_with_variances(
+                relation,
+                a_def_id,
+                opt_variances,
+                a_substs,
+                b_substs,
+                false, // do not fetch `type_of(a_def_id)`, as it will cause a cycle
+            )?;
+            Ok(tcx.mk_opaque(a_def_id, substs))
         }
 
         _ => Err(TypeError::Sorts(expected_found(relation, a, b))),
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/method_chain.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/method_chain.rs
index 13607b9079a..7e1dba4ed26 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/method_chain.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/method_chain.rs
@@ -21,10 +21,6 @@ fn tcx(&self) -> TyCtxt<'tcx> {
         self.infcx.tcx
     }
 
-    fn intercrate(&self) -> bool {
-        false
-    }
-
     fn param_env(&self) -> ty::ParamEnv<'tcx> {
         self.param_env
     }
@@ -33,10 +29,6 @@ fn a_is_expected(&self) -> bool {
         true
     }
 
-    fn mark_ambiguous(&mut self) {
-        bug!()
-    }
-
     fn relate_with_variance<T: Relate<'tcx>>(
         &mut self,
         _: ty::Variance,