diff --git a/contrib/chg/Makefile b/contrib/chg/Makefile
--- a/contrib/chg/Makefile
+++ b/contrib/chg/Makefile
@@ -5,7 +5,7 @@
 OBJS = $(SRCS:.c=.o)
 
 CFLAGS ?= -O2 -Wall -Wextra -pedantic -g
-CPPFLAGS ?= -D_FORTIFY_SOURCE=2
+CPPFLAGS ?= -D_FORTIFY_SOURCE=2 -D_GNU_SOURCE
 override CFLAGS += -std=gnu99
 ifdef HGPATH
 override CPPFLAGS += -DHGPATH=\"$(HGPATH)\"