diff --git a/src/librustdoc/clean/inline.rs b/src/librustdoc/clean/inline.rs
index 9aba399b3b0..c09c6eab4d2 100644
--- a/src/librustdoc/clean/inline.rs
+++ b/src/librustdoc/clean/inline.rs
@@ -494,7 +494,11 @@ fn separate_supertrait_bounds(mut g: clean::Generics)
 }
 
 pub fn record_extern_trait(cx: &DocContext, did: DefId) {
-    cx.external_traits.borrow_mut().entry(did).or_insert_with(|| {
-        build_external_trait(cx, did)
-    });
+    if cx.external_traits.borrow().contains_key(did) {
+        return;
+    }
+
+    let trait_ = build_external_trait(cx, did);
+
+    cx.external_traits.borrow_mut().insert(did, trait_);
 }