diff --git a/pkg/tinydtls/Makefile b/pkg/tinydtls/Makefile
index e5d6c9934e..dbe28966a9 100644
--- a/pkg/tinydtls/Makefile
+++ b/pkg/tinydtls/Makefile
@@ -5,6 +5,9 @@ PKG_VERSION=eb6f017ab451bb6cc4428b3e449955a76aeeba19
 PKG_LICENSE=EPL-1.0,EDL-1.0
 
 CFLAGS += -Wno-implicit-fallthrough
+# following is require due to known issue with newlib 2.4.x, see bug report:
+# http://lists-archives.com/cygwin/97008-gettimeofday-not-defined.html
+CFLAGS += -D_XOPEN_SOURCE=600
 
 .PHONY: all