diff --git a/winsup/cygwin/config.h.in b/winsup/cygwin/config.h.in
index 71ebe9cf5..99931a5c2 100644
--- a/winsup/cygwin/config.h.in
+++ b/winsup/cygwin/config.h.in
@@ -35,4 +35,4 @@
 #undef _MT_SAFE
 
 /* Define if using new vfork functionality. */
-#define NEWVFORK
+#undef NEWVFORK