diff --git a/networking/Makefile b/networking/Makefile
index d0427d4..98bd7f8 100644
--- a/networking/Makefile
+++ b/networking/Makefile
@@ -4,8 +4,12 @@
 #
 # Licensed under the GPL v2, see the file LICENSE in this tarball.
 
+ifndef top_srcdir
 top_srcdir=..
+endif
+ifndef top_builddir
 top_builddir=..
+endif
 srcdir=$(top_srcdir)/networking
 NETWORKING_DIR:=./
 include $(top_builddir)/Rules.mak
diff --git a/networking/libiproute/Makefile b/networking/libiproute/Makefile
index d3aefaa..96b1449 100644
--- a/networking/libiproute/Makefile
+++ b/networking/libiproute/Makefile
@@ -17,8 +17,12 @@
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 #
 
+ifndef top_srcdir
 top_srcdir=../..
+endif
+ifndef top_builddir
 top_builddir=../..
+endif
 srcdir=$(top_srcdir)/networking/libiproute
 LIBIPROUTE_DIR:=./
 include $(top_builddir)/Rules.mak
diff --git a/networking/udhcp/Makefile b/networking/udhcp/Makefile
index 3d32db5..7c027ed 100644
--- a/networking/udhcp/Makefile
+++ b/networking/udhcp/Makefile
@@ -17,8 +17,12 @@
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 #
 
+ifndef top_srcdir
 top_srcdir=../..
+endif
+ifndef top_builddir
 top_builddir=../..
+endif
 srcdir=$(top_srcdir)/networking/udhcp
 UDHCP_DIR:=./
 include $(top_builddir)/Rules.mak