diff --git a/backend/wayland/output.c b/backend/wayland/output.c
index 2d3e32696..b8760793b 100644
--- a/backend/wayland/output.c
+++ b/backend/wayland/output.c
@@ -1,3 +1,4 @@
+#define _POSIX_C_SOURCE 199309L
 #include <assert.h>
 #include <stdint.h>
 #include <stdio.h>
diff --git a/render/gles2/pixel_format.c b/render/gles2/pixel_format.c
index 5cdf8c995..fdf091f15 100644
--- a/render/gles2/pixel_format.c
+++ b/render/gles2/pixel_format.c
@@ -1,3 +1,4 @@
+#define _POSIX_C_SOURCE 199309L
 #include <drm_fourcc.h>
 #include <GLES2/gl2.h>
 #include <GLES2/gl2ext.h>
diff --git a/render/gles2/texture.c b/render/gles2/texture.c
index d66e9c161..d326da9d2 100644
--- a/render/gles2/texture.c
+++ b/render/gles2/texture.c
@@ -1,3 +1,4 @@
+#define _POSIX_C_SOURCE 199309L
 #include <assert.h>
 #include <drm_fourcc.h>
 #include <GLES2/gl2.h>
diff --git a/types/data_device/wlr_data_device.c b/types/data_device/wlr_data_device.c
index 3b5b8a668..d482a0a2c 100644
--- a/types/data_device/wlr_data_device.c
+++ b/types/data_device/wlr_data_device.c
@@ -1,3 +1,4 @@
+#define _POSIX_C_SOURCE 199309L
 #include <assert.h>
 #include <stdlib.h>
 #include <string.h>
diff --git a/types/data_device/wlr_drag.c b/types/data_device/wlr_drag.c
index 42691116e..fdbf1b8c9 100644
--- a/types/data_device/wlr_drag.c
+++ b/types/data_device/wlr_drag.c
@@ -1,3 +1,4 @@
+#define _POSIX_C_SOURCE 199309L
 #include <assert.h>
 #include <stdlib.h>
 #include <string.h>
diff --git a/types/scene/drag_icon.c b/types/scene/drag_icon.c
index b508487e0..7b4fa55b0 100644
--- a/types/scene/drag_icon.c
+++ b/types/scene/drag_icon.c
@@ -1,3 +1,4 @@
+#define _POSIX_C_SOURCE 199309L
 #include <stdlib.h>
 #include "wlr/types/wlr_compositor.h"
 #include <wlr/types/wlr_scene.h>
diff --git a/types/scene/layer_shell_v1.c b/types/scene/layer_shell_v1.c
index 67fdda287..710b709e1 100644
--- a/types/scene/layer_shell_v1.c
+++ b/types/scene/layer_shell_v1.c
@@ -1,3 +1,4 @@
+#define _POSIX_C_SOURCE 199309L
 #include <stdlib.h>
 #include <wlr/types/wlr_scene.h>
 #include <wlr/types/wlr_layer_shell_v1.h>
diff --git a/types/scene/xdg_shell.c b/types/scene/xdg_shell.c
index 9e3ffb05f..7ebef33ec 100644
--- a/types/scene/xdg_shell.c
+++ b/types/scene/xdg_shell.c
@@ -1,3 +1,4 @@
+#define _POSIX_C_SOURCE 199309L
 #include <stdlib.h>
 #include <wlr/types/wlr_scene.h>
 #include <wlr/types/wlr_xdg_shell.h>
diff --git a/types/wlr_cursor_shape_v1.c b/types/wlr_cursor_shape_v1.c
index d9f26f92b..f83fdcde2 100644
--- a/types/wlr_cursor_shape_v1.c
+++ b/types/wlr_cursor_shape_v1.c
@@ -1,3 +1,4 @@
+#define _POSIX_C_SOURCE 199309L
 #include <assert.h>
 #include <stdlib.h>
 #include <wlr/types/wlr_cursor_shape_v1.h>
diff --git a/types/wlr_export_dmabuf_v1.c b/types/wlr_export_dmabuf_v1.c
index 69245e373..d2fc574ce 100644
--- a/types/wlr_export_dmabuf_v1.c
+++ b/types/wlr_export_dmabuf_v1.c
@@ -1,3 +1,4 @@
+#define _POSIX_C_SOURCE 199309L
 #include <assert.h>
 #include <stdlib.h>
 #include <unistd.h>
diff --git a/types/wlr_idle_notify_v1.c b/types/wlr_idle_notify_v1.c
index 6283dc6a3..9997631b0 100644
--- a/types/wlr_idle_notify_v1.c
+++ b/types/wlr_idle_notify_v1.c
@@ -1,3 +1,4 @@
+#define _POSIX_C_SOURCE 199309L
 #include <assert.h>
 #include <stdlib.h>
 #include <wlr/types/wlr_idle_notify_v1.h>
diff --git a/types/wlr_keyboard.c b/types/wlr_keyboard.c
index 98978ee1d..7baad3b2e 100644
--- a/types/wlr_keyboard.c
+++ b/types/wlr_keyboard.c
@@ -1,3 +1,4 @@
+#define _POSIX_C_SOURCE 199309L
 #include <assert.h>
 #include <stdlib.h>
 #include <string.h>
diff --git a/types/wlr_keyboard_shortcuts_inhibit_v1.c b/types/wlr_keyboard_shortcuts_inhibit_v1.c
index 0e4355616..f6e17424d 100644
--- a/types/wlr_keyboard_shortcuts_inhibit_v1.c
+++ b/types/wlr_keyboard_shortcuts_inhibit_v1.c
@@ -1,3 +1,4 @@
+#define _POSIX_C_SOURCE 199309L
 #include <assert.h>
 #include <stdlib.h>
 #include <wlr/types/wlr_compositor.h>
diff --git a/types/wlr_pointer_constraints_v1.c b/types/wlr_pointer_constraints_v1.c
index f3c8fb74b..cea59b186 100644
--- a/types/wlr_pointer_constraints_v1.c
+++ b/types/wlr_pointer_constraints_v1.c
@@ -1,3 +1,4 @@
+#define _POSIX_C_SOURCE 199309L
 #include <assert.h>
 #include <limits.h>
 #include <pixman.h>
diff --git a/types/wlr_primary_selection.c b/types/wlr_primary_selection.c
index e3212d6fe..d4687b815 100644
--- a/types/wlr_primary_selection.c
+++ b/types/wlr_primary_selection.c
@@ -1,3 +1,4 @@
+#define _POSIX_C_SOURCE 199309L
 #include <assert.h>
 #include <stdlib.h>
 #include <wlr/types/wlr_primary_selection.h>
diff --git a/types/wlr_relative_pointer_v1.c b/types/wlr_relative_pointer_v1.c
index 94fb1555e..6ac846e1c 100644
--- a/types/wlr_relative_pointer_v1.c
+++ b/types/wlr_relative_pointer_v1.c
@@ -1,3 +1,4 @@
+#define _POSIX_C_SOURCE 199309L
 #include <assert.h>
 #include <inttypes.h>
 #include <stdlib.h>
diff --git a/types/wlr_screencopy_v1.c b/types/wlr_screencopy_v1.c
index 34f6c5b61..40e9577bf 100644
--- a/types/wlr_screencopy_v1.c
+++ b/types/wlr_screencopy_v1.c
@@ -1,3 +1,4 @@
+#define _POSIX_C_SOURCE 199309L
 #include <assert.h>
 #include <stdlib.h>
 #include <drm_fourcc.h>
diff --git a/types/wlr_shm.c b/types/wlr_shm.c
index ac41e87e8..4704df7a3 100644
--- a/types/wlr_shm.c
+++ b/types/wlr_shm.c
@@ -1,3 +1,6 @@
+#if !defined(__FreeBSD__)
+#define _POSIX_C_SOURCE 200112L
+#endif
 #define _DEFAULT_SOURCE // for MAP_ANONYMOUS
 #include <assert.h>
 #include <drm_fourcc.h>
diff --git a/types/wlr_transient_seat_v1.c b/types/wlr_transient_seat_v1.c
index 379ce0a37..92b18e844 100644
--- a/types/wlr_transient_seat_v1.c
+++ b/types/wlr_transient_seat_v1.c
@@ -1,3 +1,4 @@
+#define _POSIX_C_SOURCE 199309L
 #include <assert.h>
 #include <stdlib.h>
 #include <wayland-util.h>
diff --git a/types/wlr_virtual_pointer_v1.c b/types/wlr_virtual_pointer_v1.c
index 6fcd0e940..8e34b6c42 100644
--- a/types/wlr_virtual_pointer_v1.c
+++ b/types/wlr_virtual_pointer_v1.c
@@ -1,3 +1,4 @@
+#define _POSIX_C_SOURCE 199309L
 #include <assert.h>
 #include <stdlib.h>
 #include <wlr/interfaces/wlr_pointer.h>
diff --git a/types/wlr_xdg_decoration_v1.c b/types/wlr_xdg_decoration_v1.c
index d16ac7c5a..d32b15dcf 100644
--- a/types/wlr_xdg_decoration_v1.c
+++ b/types/wlr_xdg_decoration_v1.c
@@ -1,3 +1,4 @@
+#define _POSIX_C_SOURCE 199309L
 #include <assert.h>
 #include <stdbool.h>
 #include <stdlib.h>
diff --git a/types/xdg_shell/wlr_xdg_popup.c b/types/xdg_shell/wlr_xdg_popup.c
index 97e6c8e25..ffd58a613 100644
--- a/types/xdg_shell/wlr_xdg_popup.c
+++ b/types/xdg_shell/wlr_xdg_popup.c
@@ -1,3 +1,4 @@
+#define _POSIX_C_SOURCE 199309L
 #include <assert.h>
 #include <stdlib.h>
 #include <string.h>
diff --git a/types/xdg_shell/wlr_xdg_positioner.c b/types/xdg_shell/wlr_xdg_positioner.c
index 6a991bbac..dae879bbe 100644
--- a/types/xdg_shell/wlr_xdg_positioner.c
+++ b/types/xdg_shell/wlr_xdg_positioner.c
@@ -1,3 +1,4 @@
+#define _POSIX_C_SOURCE 199309L
 #include <assert.h>
 #include <stdlib.h>
 #include <wlr/util/edges.h>
diff --git a/types/xdg_shell/wlr_xdg_shell.c b/types/xdg_shell/wlr_xdg_shell.c
index 3baea04eb..d6784d1b7 100644
--- a/types/xdg_shell/wlr_xdg_shell.c
+++ b/types/xdg_shell/wlr_xdg_shell.c
@@ -1,3 +1,4 @@
+#define _POSIX_C_SOURCE 199309L
 #include <assert.h>
 #include <stdlib.h>
 #include "types/wlr_xdg_shell.h"
diff --git a/types/xdg_shell/wlr_xdg_surface.c b/types/xdg_shell/wlr_xdg_surface.c
index 029ab81a6..1e14c07ed 100644
--- a/types/xdg_shell/wlr_xdg_surface.c
+++ b/types/xdg_shell/wlr_xdg_surface.c
@@ -1,3 +1,4 @@
+#define _POSIX_C_SOURCE 199309L
 #include <assert.h>
 #include <stdlib.h>
 #include <string.h>
diff --git a/xcursor/xcursor.c b/xcursor/xcursor.c
index 7e1f310fc..17ad758bb 100644
--- a/xcursor/xcursor.c
+++ b/xcursor/xcursor.c
@@ -23,6 +23,7 @@
  * SOFTWARE.
  */
 
+#define _POSIX_C_SOURCE 200809L
 #define _DEFAULT_SOURCE
 #include <stdbool.h>
 #include <stdio.h>