--- a/configure
+++ b/configure
@@ -21,10 +21,10 @@
 datarootdir='$(prefix)/share'
 infodir='$(datarootdir)/info'
 mandir='$(datarootdir)/man'
-CXX=g++
-CPPFLAGS=
-CXXFLAGS='-Wall -W -O2'
-LDFLAGS=
+CXX?=g++
+CPPFLAGS?=
+CXXFLAGS?='-Wall -W -O2'
+LDFLAGS?=
 LIBS='-llz -lpthread'
 
 # checking whether we are using GNU C++.