diff --git a/Makefile b/Makefile
index a11c8deb89..5d2d4a10a3 100644
--- a/Makefile
+++ b/Makefile
@@ -228,7 +228,7 @@ ifeq ($(OSARCH),FreeBSD)
 endif
 
 ifeq ($(OSARCH),NetBSD)
-  _ASTCFLAGS+=-pthread -I/usr/pkg/include
+  _ASTCFLAGS+=-pthread -D__LIBPTHREAD_SOURCE__ -I/usr/pkg/include
 endif
 
 ifeq ($(OSARCH),OpenBSD)