diff --git a/include/fmt/os.h b/include/fmt/os.h
index c81955d7..3c7b3ccb 100644
--- a/include/fmt/os.h
+++ b/include/fmt/os.h
@@ -315,6 +315,7 @@ class FMT_API file {
 
   // Creates a pipe setting up read_end and write_end file objects for reading
   // and writing respectively.
+  // DEPRECATED! Taking files as out parameters is deprecated.
   static void pipe(file& read_end, file& write_end);
 
   // Creates a buffered_file object associated with this file and detaches
diff --git a/test/scan-test.cc b/test/scan-test.cc
index e2bfea3e..8c84ab06 100644
--- a/test/scan-test.cc
+++ b/test/scan-test.cc
@@ -143,6 +143,7 @@ TEST(scan_test, file) {
 }
 
 TEST(scan_test, lock) {
+
   fmt::file read_end, write_end;
   fmt::file::pipe(read_end, write_end);
 
@@ -152,6 +153,7 @@ TEST(scan_test, lock) {
     write_end.close();
   });
 
+  std::atomic<int> count = 0;
   fmt::buffered_file f = read_end.fdopen("r");
   auto fun = [&]() {
     int value = 0;
@@ -161,6 +163,7 @@ TEST(scan_test, lock) {
         EXPECT_EQ(value, 42);
         break;
       }
+      ++count;
     }
   };
   std::thread consumer1(fun);
@@ -168,5 +171,7 @@ TEST(scan_test, lock) {
   producer.join();
   consumer1.join();
   consumer2.join();
+  EXPECT_EQ(count, 1000);
+
 }
 #endif  // FMT_USE_FCNTL