diff --git a/m4/lx_check_cplex.m4 b/m4/lx_check_cplex.m4
--- a/m4/lx_check_cplex.m4
+++ b/m4/lx_check_cplex.m4
@@ -61,7 +61,7 @@
     LIBS="$lx_save_libs"
 
     if test x"$lx_cplex_found" = x"yes"; then
-      AC_DEFINE([HAVE_CPLEX], [1], [Define to 1 if you have CPLEX.])
+      AC_DEFINE([LEMON_HAVE_CPLEX], [1], [Define to 1 if you have CPLEX.])
       AC_MSG_RESULT([yes])
     else
       CPLEX_CFLAGS=""