diff --git a/src/librustc/ty/context.rs b/src/librustc/ty/context.rs
index ab1df2d4c3bb9..5e15ca16b97cd 100644
--- a/src/librustc/ty/context.rs
+++ b/src/librustc/ty/context.rs
@@ -936,8 +936,8 @@ pub struct GlobalCtxt<'tcx> {
     freevars: FxHashMap<DefId, Lrc<Vec<hir::Freevar>>>,
 
     maybe_unused_trait_imports: FxHashSet<DefId>,
-
     maybe_unused_extern_crates: Vec<(DefId, Span)>,
+    pub extern_prelude: FxHashSet<ast::Name>,
 
     // Internal cache for metadata decoding. No need to track deps on this.
     pub rcache: Lock<FxHashMap<ty::CReaderCacheKey, Ty<'tcx>>>,
@@ -1223,6 +1223,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
                     .into_iter()
                     .map(|(id, sp)| (hir.local_def_id(id), sp))
                     .collect(),
+            extern_prelude: resolutions.extern_prelude,
             hir,
             def_path_hash_to_def_id,
             queries: query::Queries::new(
diff --git a/src/librustc/ty/item_path.rs b/src/librustc/ty/item_path.rs
index ab0813240364c..ca4cafd0a7391 100644
--- a/src/librustc/ty/item_path.rs
+++ b/src/librustc/ty/item_path.rs
@@ -289,7 +289,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
                 // printing the `CrateRoot` so we don't prepend a `crate::` to paths.
                 let mut is_prelude_crate = false;
                 if let DefPathData::CrateRoot = self.def_key(parent_did).disambiguated_data.data {
-                    if self.sess.extern_prelude.contains(&data.as_interned_str().as_symbol()) {
+                    if self.extern_prelude.contains(&data.as_interned_str().as_symbol()) {
                         is_prelude_crate = true;
                     }
                 }
diff --git a/src/librustc/ty/mod.rs b/src/librustc/ty/mod.rs
index 2e8734a6aa8eb..ee6d2dfb065f0 100644
--- a/src/librustc/ty/mod.rs
+++ b/src/librustc/ty/mod.rs
@@ -36,7 +36,7 @@ use ty::subst::{Subst, Substs};
 use ty::util::{IntTypeExt, Discr};
 use ty::walk::TypeWalker;
 use util::captures::Captures;
-use util::nodemap::{NodeSet, DefIdMap, FxHashMap};
+use util::nodemap::{NodeSet, DefIdMap, FxHashMap, FxHashSet};
 use arena::SyncDroplessArena;
 use session::DataTypeKind;
 
@@ -140,6 +140,7 @@ pub struct Resolutions {
     pub maybe_unused_trait_imports: NodeSet,
     pub maybe_unused_extern_crates: Vec<(NodeId, Span)>,
     pub export_map: ExportMap,
+    pub extern_prelude: FxHashSet<Name>,
 }
 
 #[derive(Clone, Copy, PartialEq, Eq, Debug)]
diff --git a/src/librustc_driver/driver.rs b/src/librustc_driver/driver.rs
index 7fb66ea97f26b..3b0acfd6f8c12 100644
--- a/src/librustc_driver/driver.rs
+++ b/src/librustc_driver/driver.rs
@@ -790,6 +790,7 @@ where
                 trait_map: resolver.trait_map,
                 maybe_unused_trait_imports: resolver.maybe_unused_trait_imports,
                 maybe_unused_extern_crates: resolver.maybe_unused_extern_crates,
+                extern_prelude: resolver.extern_prelude,
             },
 
             analysis: ty::CrateAnalysis {
diff --git a/src/librustc_resolve/lib.rs b/src/librustc_resolve/lib.rs
index 1ad41fa058244..8cf3c0f8843a8 100644
--- a/src/librustc_resolve/lib.rs
+++ b/src/librustc_resolve/lib.rs
@@ -1360,7 +1360,7 @@ pub struct Resolver<'a, 'b: 'a> {
     graph_root: Module<'a>,
 
     prelude: Option<Module<'a>>,
-    extern_prelude: FxHashSet<Name>,
+    pub extern_prelude: FxHashSet<Name>,
 
     /// n.b. This is used only for better diagnostics, not name resolution itself.
     has_self: FxHashSet<DefId>,
diff --git a/src/librustc_typeck/check_unused.rs b/src/librustc_typeck/check_unused.rs
index 62ffffab07661..f9aa0397257b8 100644
--- a/src/librustc_typeck/check_unused.rs
+++ b/src/librustc_typeck/check_unused.rs
@@ -164,7 +164,7 @@ fn unused_crates_lint<'tcx>(tcx: TyCtxt<'_, 'tcx, 'tcx>) {
         // If the extern crate isn't in the extern prelude,
         // there is no way it can be written as an `use`.
         let orig_name = extern_crate.orig_name.unwrap_or(item.name);
-        if !tcx.sess.extern_prelude.contains(&orig_name) {
+        if !tcx.extern_prelude.contains(&orig_name) {
             continue;
         }
 
diff --git a/src/librustdoc/core.rs b/src/librustdoc/core.rs
index b85604d860be4..4a698e499a7fb 100644
--- a/src/librustdoc/core.rs
+++ b/src/librustdoc/core.rs
@@ -474,6 +474,7 @@ pub fn run_core(search_paths: SearchPaths,
             trait_map: resolver.trait_map.clone(),
             maybe_unused_trait_imports: resolver.maybe_unused_trait_imports.clone(),
             maybe_unused_extern_crates: resolver.maybe_unused_extern_crates.clone(),
+            extern_prelude: resolver.extern_prelude.clone(),
         };
         let analysis = ty::CrateAnalysis {
             access_levels: Lrc::new(AccessLevels::default()),