diff --git a/Cargo.lock b/Cargo.lock
index 52cfa2cb1f80e..ab6731e4d433d 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -3252,7 +3252,6 @@ name = "rustdoc"
 version = "0.0.0"
 dependencies = [
  "minifier 0.0.33 (registry+https://github.com/rust-lang/crates.io-index)",
- "parking_lot 0.7.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "pulldown-cmark 0.5.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "rustc-rayon 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "tempfile 3.0.5 (registry+https://github.com/rust-lang/crates.io-index)",
diff --git a/src/librustdoc/Cargo.toml b/src/librustdoc/Cargo.toml
index 334dc74c6c8f7..0eb8b73016d10 100644
--- a/src/librustdoc/Cargo.toml
+++ b/src/librustdoc/Cargo.toml
@@ -13,4 +13,3 @@ pulldown-cmark = { version = "0.5.3", default-features = false }
 minifier = "0.0.33"
 rayon = { version = "0.2.0", package = "rustc-rayon" }
 tempfile = "3"
-parking_lot = "0.7"
diff --git a/src/librustdoc/clean/inline.rs b/src/librustdoc/clean/inline.rs
index 884cdef3c771f..a8336607f7ae9 100644
--- a/src/librustdoc/clean/inline.rs
+++ b/src/librustdoc/clean/inline.rs
@@ -574,8 +574,7 @@ pub fn record_extern_trait(cx: &DocContext<'_>, did: DefId) {
     }
 
     {
-        let external_traits = cx.external_traits.lock();
-        if external_traits.borrow().contains_key(&did) ||
+        if cx.external_traits.borrow().contains_key(&did) ||
             cx.active_extern_traits.borrow().contains(&did)
         {
             return;
@@ -588,8 +587,7 @@ pub fn record_extern_trait(cx: &DocContext<'_>, did: DefId) {
     let trait_ = build_external_trait(cx, did);
 
     {
-        let external_traits = cx.external_traits.lock();
-        external_traits.borrow_mut().insert(did, trait_);
+        cx.external_traits.borrow_mut().insert(did, trait_);
     }
     cx.active_extern_traits.borrow_mut().remove_item(&did);
 }
diff --git a/src/librustdoc/clean/mod.rs b/src/librustdoc/clean/mod.rs
index 0c38e68a764f4..ee76bf35cab91 100644
--- a/src/librustdoc/clean/mod.rs
+++ b/src/librustdoc/clean/mod.rs
@@ -45,8 +45,6 @@ use std::cell::RefCell;
 use std::sync::Arc;
 use std::u32;
 
-use parking_lot::ReentrantMutex;
-
 use crate::core::{self, DocContext};
 use crate::doctree;
 use crate::html::render::{cache, ExternalLocation};
@@ -133,7 +131,7 @@ pub struct Crate {
     pub primitives: Vec<(DefId, PrimitiveType, Attributes)>,
     // These are later on moved into `CACHEKEY`, leaving the map empty.
     // Only here so that they can be filtered through the rustdoc passes.
-    pub external_traits: Arc<ReentrantMutex<RefCell<FxHashMap<DefId, Trait>>>>,
+    pub external_traits: Arc<RefCell<FxHashMap<DefId, Trait>>>,
     pub masked_crates: FxHashSet<CrateNum>,
 }
 
diff --git a/src/librustdoc/core.rs b/src/librustdoc/core.rs
index 869bec6cb88a5..6b524e1206f33 100644
--- a/src/librustdoc/core.rs
+++ b/src/librustdoc/core.rs
@@ -22,7 +22,6 @@ use syntax::json::JsonEmitter;
 use syntax::symbol::sym;
 use errors;
 use errors::emitter::{Emitter, EmitterWriter};
-use parking_lot::ReentrantMutex;
 
 use std::cell::RefCell;
 use std::mem;
@@ -50,7 +49,7 @@ pub struct DocContext<'tcx> {
     /// Later on moved into `html::render::CACHE_KEY`
     pub renderinfo: RefCell<RenderInfo>,
     /// Later on moved through `clean::Crate` into `html::render::CACHE_KEY`
-    pub external_traits: Arc<ReentrantMutex<RefCell<FxHashMap<DefId, clean::Trait>>>>,
+    pub external_traits: Arc<RefCell<FxHashMap<DefId, clean::Trait>>>,
     /// Used while populating `external_traits` to ensure we don't process the same trait twice at
     /// the same time.
     pub active_extern_traits: RefCell<Vec<DefId>>,
diff --git a/src/librustdoc/fold.rs b/src/librustdoc/fold.rs
index cfa22bc27b758..5482239c7ce28 100644
--- a/src/librustdoc/fold.rs
+++ b/src/librustdoc/fold.rs
@@ -105,12 +105,12 @@ pub trait DocFolder : Sized {
         c.module = c.module.take().and_then(|module| self.fold_item(module));
 
         {
-            let guard = c.external_traits.lock();
-            let traits = guard.replace(Default::default());
-            guard.borrow_mut().extend(traits.into_iter().map(|(k, mut v)| {
+            let mut guard = c.external_traits.borrow_mut();
+            let external_traits = std::mem::replace(&mut *guard, Default::default());
+            *guard = external_traits.into_iter().map(|(k, mut v)| {
                 v.items = v.items.into_iter().filter_map(|i| self.fold_item(i)).collect();
                 (k, v)
-            }));
+            }).collect();
         }
         c
     }
diff --git a/src/librustdoc/html/render.rs b/src/librustdoc/html/render.rs
index b1cee0182052b..211f1e325b9ec 100644
--- a/src/librustdoc/html/render.rs
+++ b/src/librustdoc/html/render.rs
@@ -659,7 +659,7 @@ pub fn run(mut krate: clean::Crate,
         crate_version: krate.version.take(),
         orphan_impl_items: Vec::new(),
         orphan_trait_impls: Vec::new(),
-        traits: krate.external_traits.lock().replace(Default::default()),
+        traits: krate.external_traits.replace(Default::default()),
         deref_trait_did,
         deref_mut_trait_did,
         owned_box_did,