diff --git a/src/corelib/CMakeLists.txt b/src/corelib/CMakeLists.txt
index daf98e929a..c9e788054f 100644
--- a/src/corelib/CMakeLists.txt
+++ b/src/corelib/CMakeLists.txt
@@ -1000,7 +1000,7 @@ qt_internal_extend_target(Core CONDITION QT_FEATURE_filesystemiterator AND WIN32
 qt_internal_extend_target(Core CONDITION QT_FEATURE_process AND UNIX
     SOURCES
         ../3rdparty/forkfd/forkfd.h
-        io/forkfd_qt.cpp
+        io/forkfd_qt.c
     INCLUDE_DIRECTORIES
         ../3rdparty/forkfd
 )
diff --git a/src/corelib/io/forkfd_qt.cpp b/src/corelib/io/forkfd_qt.c
similarity index 87%
rename from src/corelib/io/forkfd_qt.cpp
rename to src/corelib/io/forkfd_qt.c
index 3c6d05d6a8..7107b2c6a0 100644
--- a/src/corelib/io/forkfd_qt.cpp
+++ b/src/corelib/io/forkfd_qt.c
@@ -1,6 +1,9 @@
 // Copyright (C) 2016 Intel Corporation.
 // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
 
+#ifndef _GNU_SOURCE
+#  define _GNU_SOURCE
+#endif
 #include <QtCore/qglobal.h>
 
 #define FORKFD_NO_SPAWNFD