diff --git a/compiler/rustc_ast_lowering/src/lib.rs b/compiler/rustc_ast_lowering/src/lib.rs
index 7202774292f..a9950b82928 100644
--- a/compiler/rustc_ast_lowering/src/lib.rs
+++ b/compiler/rustc_ast_lowering/src/lib.rs
@@ -44,7 +44,6 @@ use rustc_ast::{self as ast, *};
 use rustc_ast_pretty::pprust;
 use rustc_data_structures::captures::Captures;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
-use rustc_data_structures::stable_hasher::StableVec;
 use rustc_data_structures::sync::Lrc;
 use rustc_errors::{struct_span_err, Applicability};
 use rustc_hir as hir;
@@ -506,7 +505,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         for (k, v) in self.resolver.trait_map().into_iter() {
             if let Some(Some(hir_id)) = self.node_id_to_hir_id.get(k) {
                 let map = trait_map.entry(hir_id.owner).or_default();
-                map.insert(hir_id.local_id, StableVec::new(v.to_vec()));
+                map.insert(hir_id.local_id, v.into_boxed_slice());
             }
         }
 
diff --git a/compiler/rustc_data_structures/src/stable_hasher.rs b/compiler/rustc_data_structures/src/stable_hasher.rs
index ff28784a1dc..18b352cf3b0 100644
--- a/compiler/rustc_data_structures/src/stable_hasher.rs
+++ b/compiler/rustc_data_structures/src/stable_hasher.rs
@@ -550,35 +550,3 @@ pub fn hash_stable_hashmap<HCX, K, V, R, SK, F>(
     entries.sort_unstable_by(|&(ref sk1, _), &(ref sk2, _)| sk1.cmp(sk2));
     entries.hash_stable(hcx, hasher);
 }
-
-/// A vector container that makes sure that its items are hashed in a stable
-/// order.
-#[derive(Debug)]
-pub struct StableVec<T>(Vec<T>);
-
-impl<T> StableVec<T> {
-    pub fn new(v: Vec<T>) -> Self {
-        StableVec(v)
-    }
-}
-
-impl<T> ::std::ops::Deref for StableVec<T> {
-    type Target = Vec<T>;
-
-    fn deref(&self) -> &Vec<T> {
-        &self.0
-    }
-}
-
-impl<T, HCX> HashStable<HCX> for StableVec<T>
-where
-    T: HashStable<HCX> + ToStableHashKey<HCX>,
-{
-    fn hash_stable(&self, hcx: &mut HCX, hasher: &mut StableHasher) {
-        let StableVec(ref v) = *self;
-
-        let mut sorted: Vec<_> = v.iter().map(|x| x.to_stable_hash_key(hcx)).collect();
-        sorted.sort_unstable();
-        sorted.hash_stable(hcx, hasher);
-    }
-}
diff --git a/compiler/rustc_hir/src/hir.rs b/compiler/rustc_hir/src/hir.rs
index 8600276f05d..e9055c95410 100644
--- a/compiler/rustc_hir/src/hir.rs
+++ b/compiler/rustc_hir/src/hir.rs
@@ -11,7 +11,6 @@ pub use rustc_ast::{BorrowKind, ImplPolarity, IsAuto};
 pub use rustc_ast::{CaptureBy, Movability, Mutability};
 use rustc_ast::{InlineAsmOptions, InlineAsmTemplatePiece};
 use rustc_data_structures::fx::FxHashMap;
-use rustc_data_structures::stable_hasher::StableVec;
 use rustc_data_structures::sync::{par_for_each_in, Send, Sync};
 use rustc_macros::HashStable_Generic;
 use rustc_span::source_map::Spanned;
@@ -662,7 +661,7 @@ pub struct Crate<'hir> {
 
     /// Map indicating what traits are in scope for places where this
     /// is relevant; generated by resolve.
-    pub trait_map: FxHashMap<LocalDefId, FxHashMap<ItemLocalId, StableVec<TraitCandidate>>>,
+    pub trait_map: FxHashMap<LocalDefId, FxHashMap<ItemLocalId, Box<[TraitCandidate]>>>,
 
     /// Collected attributes from HIR nodes.
     pub attrs: BTreeMap<HirId, &'hir [Attribute]>,
diff --git a/compiler/rustc_middle/src/query/mod.rs b/compiler/rustc_middle/src/query/mod.rs
index 90be88e1936..3cc8fc3fe31 100644
--- a/compiler/rustc_middle/src/query/mod.rs
+++ b/compiler/rustc_middle/src/query/mod.rs
@@ -1127,7 +1127,7 @@ rustc_queries! {
         desc { "computing whether impls specialize one another" }
     }
     query in_scope_traits_map(_: LocalDefId)
-        -> Option<&'tcx FxHashMap<ItemLocalId, StableVec<TraitCandidate>>> {
+        -> Option<&'tcx FxHashMap<ItemLocalId, Box<[TraitCandidate]>>> {
         desc { "traits in scope at a block" }
     }
 
diff --git a/compiler/rustc_middle/src/ty/context.rs b/compiler/rustc_middle/src/ty/context.rs
index 19a768689b8..ef93f4f64d8 100644
--- a/compiler/rustc_middle/src/ty/context.rs
+++ b/compiler/rustc_middle/src/ty/context.rs
@@ -31,7 +31,7 @@ use rustc_attr as attr;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_data_structures::profiling::SelfProfilerRef;
 use rustc_data_structures::sharded::{IntoPointer, ShardedHashMap};
-use rustc_data_structures::stable_hasher::{HashStable, StableHasher, StableVec};
+use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_data_structures::steal::Steal;
 use rustc_data_structures::sync::{self, Lock, Lrc, WorkerLocal};
 use rustc_errors::ErrorReported;
@@ -2651,8 +2651,10 @@ impl<'tcx> TyCtxt<'tcx> {
         struct_lint_level(self.sess, lint, level, src, None, decorate);
     }
 
-    pub fn in_scope_traits(self, id: HirId) -> Option<&'tcx StableVec<TraitCandidate>> {
-        self.in_scope_traits_map(id.owner).and_then(|map| map.get(&id.local_id))
+    pub fn in_scope_traits(self, id: HirId) -> Option<&'tcx [TraitCandidate]> {
+        let map = self.in_scope_traits_map(id.owner)?;
+        let candidates = map.get(&id.local_id)?;
+        Some(&*candidates)
     }
 
     pub fn named_region(self, id: HirId) -> Option<resolve_lifetime::Region> {
diff --git a/compiler/rustc_middle/src/ty/query/mod.rs b/compiler/rustc_middle/src/ty/query/mod.rs
index bec13da017e..a5b540dcb70 100644
--- a/compiler/rustc_middle/src/ty/query/mod.rs
+++ b/compiler/rustc_middle/src/ty/query/mod.rs
@@ -34,7 +34,6 @@ use crate::ty::subst::{GenericArg, SubstsRef};
 use crate::ty::util::AlwaysRequiresDrop;
 use crate::ty::{self, AdtSizedConstraint, CrateInherentImpls, ParamEnvAnd, Ty, TyCtxt};
 use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexMap};
-use rustc_data_structures::stable_hasher::StableVec;
 use rustc_data_structures::steal::Steal;
 use rustc_data_structures::svh::Svh;
 use rustc_data_structures::sync::Lrc;