diff --git a/configure b/configure
index e9131851..f3e75b4c 100755
--- a/configure
+++ b/configure
@@ -1683,6 +1683,7 @@ ac_link='$CC -o conftest$ac_exeext $CFLAGS $CPPFLAGS $LDFLAGS conftest.$ac_ext $
 ac_compiler_gnu=$ac_cv_c_compiler_gnu
 
 
+SAVED_CXXFLAGS=$CXXFLAGS
 ac_ext=cpp
 ac_cpp='$CXXCPP $CPPFLAGS'
 ac_compile='$CXX -c $CXXFLAGS $CPPFLAGS conftest.$ac_ext >&5'
@@ -2405,7 +2406,7 @@ case $host_os in *\ *) host_os=`echo "$host_os" | sed 's/ /-/g'`;; esac
 
 
 
-CXXFLAGS="$CXXFLAGS -D_GNU_SOURCE"
+CXXFLAGS="$SAVED_CXXFLAGS -D_GNU_SOURCE"
 INCLUDES=""
 LIBS=""
 DEPEND=""
diff --git a/configure.in b/configure.in
index a72a0067..0e64ccd9 100644
--- a/configure.in
+++ b/configure.in
@@ -1,9 +1,10 @@
 dnl Keep the version number in sync with main.h!
 AC_INIT([znc], [0.051])
+SAVED_CXXFLAGS=$CXXFLAGS
 AC_PROG_CXX
 AC_CANONICAL_HOST
 
-CXXFLAGS="$CXXFLAGS -D_GNU_SOURCE"
+CXXFLAGS="$SAVED_CXXFLAGS -D_GNU_SOURCE"
 INCLUDES=""
 LIBS=""
 DEPEND=""