--- a/Makefile
+++ b/Makefile
@@ -6,8 +6,11 @@
 LIBDIR=$(DESTDIR)/usr/lib
 INSTALL=install
 
+CPPFLAGS:=$(shell dpkg-buildflags --get CPPFLAGS)
 # You may need to change the -I arguments depending on your system
-CFLAGS=-O3 -I/usr/include/tcl8.6
+CFLAGS:=-O3 -I/usr/include/tcl8.6 $(shell dpkg-buildflags --get CFLAGS)
+CXXFLAGS:=$(shell dpkg-buildflags --get CXXFLAGS)
+LDFLAGS:=$(shell dpkg-buildflags --get LDFLAGS)
 
 SOFLAGS = -fPIC -Wl,-soname,libfilecmp.so.0.0
 
