diff --git a/package/network/utils/iperf3/Makefile b/package/network/utils/iperf3/Makefile
index 3d9c84ae25b69c2927a09450a1b96b13711117ec..f36b381dacc768d6c0849391a7dafd3993d89525 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=