--- feh-2.23/config.mk	2017-12-28 18:28:35.000000000 +0000
+++ feh-2.23/config.mk	2018-01-08 01:19:54.440000000 +0000
@@ -38,7 +38,7 @@
 CFLAGS += -Wall -Wextra -pedantic
 
 # Settings for glibc >= 2.19 - may need to be adjusted for other systems
-CFLAGS += -std=c11 -D_POSIX_C_SOURCE=200809L -D_XOPEN_SOURCE=500
+CFLAGS += -std=c11 -D_POSIX_C_SOURCE=200809L -D_XOPEN_SOURCE=700
 
 ifeq (${curl},1)
 	CFLAGS += -DHAVE_LIBCURL