diff --git a/tests/common/mod.rs b/tests/common/mod.rs
index ecf4f88..0f83f1c 100644
--- a/tests/common/mod.rs
+++ b/tests/common/mod.rs
@@ -13,7 +13,8 @@
     ($($tt:tt)*) => {
         {
             use ::std::io::Write;
-            write!(::std::io::stderr(), $($tt)*).unwrap();
+            let stderr = ::std::io::stderr();
+            write!(stderr.lock(), $($tt)*).unwrap();
         }
     };
 }