diff --git a/src/corelib/io/qlockfile_unix.cpp b/src/corelib/io/qlockfile_unix.cpp
index b2bf77c0da8..ce2b7e8faa8 100644
--- a/src/corelib/io/qlockfile_unix.cpp
+++ b/src/corelib/io/qlockfile_unix.cpp
@@ -58,7 +58,8 @@
 #include <sys/file.h>  // flock
 #endif
 
-#if defined(Q_OS_RTEMS)
+#if defined(Q_OS_RTEMS) || defined(Q_OS_QNX)
+// flock() does not work in these OSes and produce warnings when we try to use
 #  undef LOCK_EX
 #  undef LOCK_NB
 #endif