--- a/configure
+++ b/configure
@@ -38,8 +38,8 @@
   return 0;
 }
 EOF
-CXX=unknown;
-for i in "CC" "g++" "cc" "$CC"; do
+CXX=${CXX-unknown}
+for i in "$CXX" "CC" "g++" "cc"; do
   if $i -c $tmp_file.C 2>/dev/null; then
     CXX="$i";
     break;