diff --git a/Makefile.am b/Makefile.am
--- a/Makefile.am
+++ b/Makefile.am
@@ -1,5 +1,7 @@
 ACLOCAL_AMFLAGS = -I m4
 
+AM_CXXFLAGS = $(WARNINGCXXFLAGS)
+
 AM_CPPFLAGS = -I$(top_srcdir) -I$(top_builddir)
 LDADD = $(top_builddir)/lemon/libemon.la
 
diff --git a/configure.ac b/configure.ac
--- a/configure.ac
+++ b/configure.ac
@@ -19,8 +19,6 @@
 AC_CONFIG_SRCDIR([lemon/list_graph.h])
 AC_CONFIG_HEADERS([config.h lemon/config.h])
 
-lx_cmdline_cxxflags_set=${CXXFLAGS+set}
-
 dnl Do compilation tests using the C++ compiler.
 AC_LANG([C++])
 
@@ -46,9 +44,10 @@
 fi
 
 dnl Set custom compiler flags when using g++.
-if test x"$lx_cmdline_cxxflags_set" != x"set" -a "$GXX" = yes -a "$ICC" = no; then
-  CXXFLAGS="$CXXFLAGS -Wall -W -Wall -W -Wunused -Wformat=2 -Wctor-dtor-privacy -Wnon-virtual-dtor -Wno-char-subscripts -Wwrite-strings -Wno-char-subscripts -Wreturn-type -Wcast-qual -Wcast-align -Wsign-promo -Woverloaded-virtual -Woverloaded-virtual -ansi -fno-strict-aliasing -Wold-style-cast -Wno-unknown-pragmas"
+if test "$GXX" = yes -a "$ICC" = no; then
+  WARNINGCXXFLAGS="-Wall -W -Wall -W -Wunused -Wformat=2 -Wctor-dtor-privacy -Wnon-virtual-dtor -Wno-char-subscripts -Wwrite-strings -Wno-char-subscripts -Wreturn-type -Wcast-qual -Wcast-align -Wsign-promo -Woverloaded-virtual -ansi -fno-strict-aliasing -Wold-style-cast -Wno-unknown-pragmas"
 fi
+AC_SUBST([WARNINGCXXFLAGS])
 
 dnl Checks for libraries.
 #LX_CHECK_GLPK
@@ -113,7 +112,7 @@
 echo Package version............... : $PACKAGE-$VERSION
 echo
 echo C++ compiler.................. : $CXX
-echo C++ compiles flags............ : $CXXFLAGS
+echo C++ compiles flags............ : $WARNINGCXXFLAGS $CXXFLAGS
 echo
 #echo GLPK support.................. : $lx_glpk_found
 #echo CPLEX support................. : $lx_cplex_found
diff --git a/lemon/Makefile.am b/lemon/Makefile.am
--- a/lemon/Makefile.am
+++ b/lemon/Makefile.am
@@ -12,7 +12,7 @@
         lemon/color.cc \
         lemon/random.cc
 
-#lemon_libemon_la_CXXFLAGS = $(GLPK_CFLAGS) $(CPLEX_CFLAGS) $(SOPLEX_CXXFLAGS)
+#lemon_libemon_la_CXXFLAGS = $(GLPK_CFLAGS) $(CPLEX_CFLAGS) $(SOPLEX_CXXFLAGS) $(AM_CXXFLAGS)
 #lemon_libemon_la_LDFLAGS = $(GLPK_LIBS) $(CPLEX_LIBS) $(SOPLEX_LIBS)
 
 lemon_HEADERS += \