diff --git a/Makefile.am b/Makefile.am
index 8cd56d1..a8da8d6 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -5,6 +5,7 @@ WARN_CLANG=-Wformat-nonliteral -Wstrncat-size -Wformat-security -Wsign-conversio
 WARN_GCC=-Wformat=2 -Wformat-overflow=2 -Wformat-nonliteral -Wformat-truncation=2 -Wnull-dereference -Wstrict-overflow=2 -Wstringop-overflow=4 -Walloca-larger-than=4096 -Wtype-limits -Wconversion -Wtrampolines -Wstrict-prototypes -Wmissing-prototypes -Wmissing-declarations -fno-common -Wcast-align
 CFLAGS ?= -g
 OPTS=-I. -O3 $(CFLAGS) -fcommon
+CPPFLAGS += -D_GNU_SOURCE
 # -Wall -g -pedantic
 LIBS=-lm
 DESTDIR ?=