diff --git a/tools/iio/Makefile b/tools/iio/Makefile
index 83813ad..bf7ae6d 100644
--- a/tools/iio/Makefile
+++ b/tools/iio/Makefile
@@ -1,5 +1,5 @@
 CC = gcc
-CFLAGS = -Wall -g
+CFLAGS = -Wall -g -D_GNU_SOURCE
 
 all: iio_event_monitor lsiio generic_buffer