diff --git a/package/network/utils/iperf3/Makefile b/package/network/utils/iperf3/Makefile
index 3d9c84ae25..f36b381dac 100644
--- a/package/network/utils/iperf3/Makefile
+++ b/package/network/utils/iperf3/Makefile
@@ -30,6 +30,7 @@ define Package/iperf3
   URL:=http://sourceforge.net/projects/iperf/
 endef
 
+TARGET_CFLAGS += -D_GNU_SOURCE
 CONFIGURE_ARGS += --disable-shared
 
 MAKE_FLAGS += noinst_PROGRAMS=