diff --git a/tests/run-pass/concurrency/concurrent_caller_location.rs b/tests/run-pass/concurrency/concurrent_caller_location.rs
index e3e2f9ac60ae..d509d1b3f797 100644
--- a/tests/run-pass/concurrency/concurrent_caller_location.rs
+++ b/tests/run-pass/concurrency/concurrent_caller_location.rs
@@ -1,3 +1,5 @@
+// ignore-windows: Concurrency on Windows is not supported yet.
+
 use std::thread::spawn;
 use std::panic::Location;
 
diff --git a/tests/run-pass/concurrency/issue1643.rs b/tests/run-pass/concurrency/issue1643.rs
index c0956569ad8f..1238a1bd6f5e 100644
--- a/tests/run-pass/concurrency/issue1643.rs
+++ b/tests/run-pass/concurrency/issue1643.rs
@@ -1,3 +1,5 @@
+// ignore-windows: Concurrency on Windows is not supported yet.
+
 use std::thread::spawn;
 
 fn initialize() {