diff --git a/makefile.vc b/makefile.vc
index 1f790f0de..2f7e00f7b 100644
--- a/makefile.vc
+++ b/makefile.vc
@@ -17,11 +17,11 @@ LIBOBJ	 = src\box2d.obj src\bytebuffer.obj src\g_box.obj \
 	src\rtout_kml.obj src\rtout_svg.obj src\rtout_twkb.obj src\rtout_wkb.obj \
 	src\rtout_wkt.obj src\rtout_x3d.obj src\rtpoint.obj src\rtpoly.obj src\rtprint.obj \
 	src\rtpsurface.obj src\rtspheroid.obj src\rtstroke.obj src\rttin.obj src\rttree.obj \
-	src\rttriangle.obj src\rtutil.obj src\stringbuffer.obj src\varint.obj
+	src\rttriangle.obj src\rtutil.obj src\stringbuffer.obj src\varint.obj src\rtt_tpsnap.obj
 
 LIBRTTOPO_DLL	 	       =	librttopo$(VERSION).dll
 
-CFLAGS	=	/nologo -IC:\OSGeo4W\include -I. -Iheaders $(OPTFLAGS)
+CFLAGS	=	/nologo -I. -Iheaders $(OPTFLAGS)
 
 default:	all
 

diff --git a/nmake.opt b/nmake.opt
index 938979df1..ea80dab00 100644
--- a/nmake.opt
+++ b/nmake.opt
@@ -1,9 +1,8 @@
 # Directory tree where RTTOPO will be installed.
-INSTDIR=C:\OSGeo4W
+INSTDIR=$(INSTALLDIR)
 
 # Uncomment the first for an optimized build, or the second for debug.
-OPTFLAGS=	/nologo /Ox /fp:precise /W4 /MD /D_CRT_SECURE_NO_WARNINGS \
-			/DDLL_EXPORT
+OPTFLAGS=	/nologo /fp:precise /W4 $(CL_FLAGS) /D_CRT_SECURE_NO_WARNINGS
 #OPTFLAGS=	/nologo /Zi /MD /Fdlibrttopo.pdb /DDLL_EXPORT
 
 # Set the version number for the DLL.  Normally we leave this blank since