diff --git a/rust-version b/rust-version
index 81fe678f1172..be7b603f9054 100644
--- a/rust-version
+++ b/rust-version
@@ -1 +1 @@
-0a675c5e02e6ecfda7d4e04aabd23a9935e0c4bf
+ff4df04799c406c8149a041c3163321758aac924
diff --git a/src/shims/foreign_items/windows.rs b/src/shims/foreign_items/windows.rs
index a58444b21bff..f55b5b8450e0 100644
--- a/src/shims/foreign_items/windows.rs
+++ b/src/shims/foreign_items/windows.rs
@@ -236,12 +236,14 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
             | "LeaveCriticalSection"
             | "DeleteCriticalSection" if this.frame().instance.to_string().starts_with("std::sys::windows::")
             => {
+                assert_eq!(this.get_total_thread_count()?, 1, "concurrency on Windows not supported");
                 // Nothing to do, not even a return value.
                 // (Windows locks are reentrant, and we have only 1 thread,
                 // so not doing any futher checks here is at least not incorrect.)
             }
             "TryEnterCriticalSection" if this.frame().instance.to_string().starts_with("std::sys::windows::")
             => {
+                assert_eq!(this.get_total_thread_count()?, 1, "concurrency on Windows not supported");
                 // There is only one thread, so this always succeeds and returns TRUE
                 this.write_scalar(Scalar::from_i32(1), dest)?;
             }
diff --git a/tests/run-pass/sync.rs b/tests/run-pass/sync_singlethread.rs
similarity index 100%
rename from tests/run-pass/sync.rs
rename to tests/run-pass/sync_singlethread.rs