diff --git a/library/std/src/backtrace.rs b/library/std/src/backtrace.rs
index 18d5f3e910838..f0e199fac737c 100644
--- a/library/std/src/backtrace.rs
+++ b/library/std/src/backtrace.rs
@@ -140,6 +140,11 @@ struct Capture {
     frames: Vec<BacktraceFrame>,
 }
 
+fn _assert_send_sync() {
+    fn _assert<T: Send + Sync>() {}
+    _assert::<Backtrace>();
+}
+
 /// A single frame of a backtrace.
 #[unstable(feature = "backtrace_frames", issue = "79676")]
 pub struct BacktraceFrame {
@@ -422,7 +427,7 @@ impl fmt::Display for Backtrace {
     }
 }
 
-type LazyResolve = impl FnOnce() -> Capture;
+type LazyResolve = impl (FnOnce() -> Capture) + Send + Sync;
 
 fn lazy_resolve(mut capture: Capture) -> LazyResolve {
     move || {
diff --git a/library/std/tests/backtrace.rs b/library/std/tests/backtrace.rs
deleted file mode 100644
index 531c5f89cf67f..0000000000000
--- a/library/std/tests/backtrace.rs
+++ /dev/null
@@ -1,10 +0,0 @@
-use std::backtrace::Backtrace;
-
-// Unfortunately, this cannot be a unit test because that causes problems
-// with type-alias-impl-trait (the assert counts as a defining use).
-#[test]
-fn assert_send_sync() {
-    fn assert<T: Send + Sync>() {}
-
-    assert::<Backtrace>();
-}