diff --git a/winsup/cygwin/thread.cc b/winsup/cygwin/thread.cc
index 963c4017b..909940773 100644
--- a/winsup/cygwin/thread.cc
+++ b/winsup/cygwin/thread.cc
@@ -1426,7 +1426,7 @@ pthread_rwlock::rdlock (PLARGE_INTEGER timeout)
       if (reader->n < UINT32_MAX)
 	++reader->n;
       else
-	errno = EAGAIN;
+	result = EAGAIN;
       goto DONE;
     }