diff --git a/acx_nlnetlabs.m4 b/acx_nlnetlabs.m4
index 26513e4ff..8d889f545 100644
--- a/acx_nlnetlabs.m4
+++ b/acx_nlnetlabs.m4
@@ -421,12 +421,13 @@ AC_DEFUN([ACX_CHECK_FLTO], [
     AS_IF([test "x$enable_flto" != "xno"], [
         AC_MSG_CHECKING([if $CC supports -flto])
         BAKCFLAGS="$CFLAGS"
-        CFLAGS="$CFLAGS -flto"
+        CFLAGS="$CFLAGS -flto -Werror"
         AC_LINK_IFELSE([AC_LANG_PROGRAM([], [])], [
             if $CC $CFLAGS -o conftest conftest.c 2>&1 | grep "warning: no debug symbols in executable" >/dev/null; then
                 CFLAGS="$BAKCFLAGS"
                 AC_MSG_RESULT(no)
             else
+                CFLAGS="$CFLAGS -flto"
                 AC_MSG_RESULT(yes)
             fi
             rm -f conftest conftest.c conftest.o
diff --git a/configure b/configure
index 2b766c984..897ac7d07 100755
--- a/configure
+++ b/configure
@@ -5859,7 +5859,7 @@ fi
         { $as_echo "$as_me:${as_lineno-$LINENO}: checking if $CC supports -flto" >&5
 $as_echo_n "checking if $CC supports -flto... " >&6; }
         BAKCFLAGS="$CFLAGS"
-        CFLAGS="$CFLAGS -flto"
+        CFLAGS="$CFLAGS -flto -Werror"
         cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -5878,6 +5878,7 @@ if ac_fn_c_try_link "$LINENO"; then :
                 { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
 $as_echo "no" >&6; }
             else
+                CFLAGS="$CFLAGS -flto"
                 { $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
 $as_echo "yes" >&6; }
             fi