diff --git a/src/libsysprof-capture/sysprof-capture-writer.c b/src/libsysprof-capture/sysprof-capture-writer.c
index f890da98..14577aaf 100644
--- a/src/libsysprof-capture/sysprof-capture-writer.c
+++ b/src/libsysprof-capture/sysprof-capture-writer.c
@@ -56,10 +56,6 @@
 
 #include "config.h"
 
-#ifndef _GNU_SOURCE
-# define _GNU_SOURCE
-#endif
-
 #include <assert.h>
 #include <endian.h>
 #include <errno.h>
diff --git a/src/libsysprof-capture/sysprof-collector.c b/src/libsysprof-capture/sysprof-collector.c
index 6d9e6b1c..9ffa9aae 100644
--- a/src/libsysprof-capture/sysprof-collector.c
+++ b/src/libsysprof-capture/sysprof-collector.c
@@ -54,10 +54,6 @@
  * SPDX-License-Identifier: BSD-2-Clause-Patent
  */
 
-#ifndef _GNU_SOURCE
-# define _GNU_SOURCE
-#endif
-
 #include <assert.h>
 #include <errno.h>
 #include <poll.h>
diff --git a/src/libsysprof-ui/sysprof-details-page.c b/src/libsysprof-ui/sysprof-details-page.c
index 0c41ec46..8755f0e9 100644
--- a/src/libsysprof-ui/sysprof-details-page.c
+++ b/src/libsysprof-ui/sysprof-details-page.c
@@ -18,10 +18,6 @@
  * SPDX-License-Identifier: GPL-3.0-or-later
  */
 
-#ifndef _GNU_SOURCE
-# define _GNU_SOURCE
-#endif
-
 #define G_LOG_DOMAIN "sysprof-details-page"
 
 #include "config.h"
diff --git a/src/libsysprof-ui/sysprof-profiler-assistant.c b/src/libsysprof-ui/sysprof-profiler-assistant.c
index 069f3c91..89e35137 100644
--- a/src/libsysprof-ui/sysprof-profiler-assistant.c
+++ b/src/libsysprof-ui/sysprof-profiler-assistant.c
@@ -20,10 +20,6 @@
 
 #define G_LOG_DOMAIN "sysprof-profiler-assistant"
 
-#ifndef _GNU_SOURCE
-# define _GNU_SOURCE
-#endif
-
 #include "config.h"
 
 #include <sysprof.h>
diff --git a/src/libsysprof/preload/backtrace-helper.h b/src/libsysprof/preload/backtrace-helper.h
index 1915a420..92792a56 100644
--- a/src/libsysprof/preload/backtrace-helper.h
+++ b/src/libsysprof/preload/backtrace-helper.h
@@ -20,10 +20,6 @@
 
 #pragma once
 
-#ifndef _GNU_SOURCE
-# define _GNU_SOURCE
-#endif
-
 #ifdef HAVE_EXECINFO_H
 # include <execinfo.h>
 #endif
diff --git a/src/libsysprof/preload/sysprof-memory-collector.c b/src/libsysprof/preload/sysprof-memory-collector.c
index 72cf0515..19cf2c60 100644
--- a/src/libsysprof/preload/sysprof-memory-collector.c
+++ b/src/libsysprof/preload/sysprof-memory-collector.c
@@ -18,8 +18,6 @@
  * SPDX-License-Identifier: GPL-3.0-or-later
  */
 
-#define _GNU_SOURCE
-
 #include "config.h"
 
 #include <dlfcn.h>
diff --git a/src/libsysprof/preload/sysprof-speedtrack-collector.c b/src/libsysprof/preload/sysprof-speedtrack-collector.c
index 223dea91..62f75a68 100644
--- a/src/libsysprof/preload/sysprof-speedtrack-collector.c
+++ b/src/libsysprof/preload/sysprof-speedtrack-collector.c
@@ -18,8 +18,6 @@
  * SPDX-License-Identifier: GPL-3.0-or-later
  */
 
-#define _GNU_SOURCE
-
 #include "config.h"
 
 #include <dlfcn.h>
diff --git a/src/libsysprof/sysprof-kallsyms.c b/src/libsysprof/sysprof-kallsyms.c
index 965d1cca..4545fba0 100644
--- a/src/libsysprof/sysprof-kallsyms.c
+++ b/src/libsysprof/sysprof-kallsyms.c
@@ -22,10 +22,6 @@
 
 #include "config.h"
 
-#ifndef _GNU_SOURCE
-# define _GNU_SOURCE
-#endif
-
 #include <errno.h>
 #include <string.h>
 #include <stdio.h>
diff --git a/src/sysprofd/sysprof-turbostat.c b/src/sysprofd/sysprof-turbostat.c
index 5c80a534..72d6d674 100644
--- a/src/sysprofd/sysprof-turbostat.c
+++ b/src/sysprofd/sysprof-turbostat.c
@@ -18,8 +18,6 @@
  * SPDX-License-ntifier: GPL-3.0-or-later
  */
 
-#define _GNU_SOURCE
-
 #include "sysprof-turbostat.h"
 
 #include <errno.h>