diff --git a/configure.ac b/configure.ac
index f64e25f4..96693d9c 100644
--- a/configure.ac
+++ b/configure.ac
@@ -44,8 +44,13 @@ AC_PROG_CC_C99
 AC_PROG_INSTALL
 AC_HEADER_STDC
 
+extra_flags="-Wformat-security		\
+             -Wstack-protector		\
+	     -Wstack-protector-all	\
+	     -Wno-cast-function-type"
+
 AX_CXX_COMPILE_STDCXX_14
-m4_ifdef([AX_COMPILER_FLAGS],[AX_COMPILER_FLAGS(,,[yes])])
+m4_ifdef([AX_COMPILER_FLAGS],[AX_COMPILER_FLAGS(,,[yes],${extra_flags})])
 AX_VALGRIND_CHECK
 
 # for now, use AM_PROG_LIBTOOL, as we don't want to require
diff --git a/guile/Makefile.am b/guile/Makefile.am
index e63c1b06..15ca95cb 100644
--- a/guile/Makefile.am
+++ b/guile/Makefile.am
@@ -28,8 +28,8 @@ AM_CPPFLAGS=						\
 # don't use -Werror, as it might break on other compilers
 # use -Wno-unused-parameters, because some callbacks may not
 # really need all the params they get
-AM_CFLAGS=-Wall -Wextra -Wno-unused-parameter -Wdeclaration-after-statement
-AM_CXXFLAGS=-Wall -Wextra -Wno-unused-parameter
+AM_CFLAGS=${WARN_CFLAGS}
+AM_CXXFLAGS=${WARN_CXXFLAGS}
 
 lib_LTLIBRARIES=					\
 	libguile-mu.la
diff --git a/mu/tests/Makefile.am b/mu/tests/Makefile.am
index 818f59f4..565f4703 100644
--- a/mu/tests/Makefile.am
+++ b/mu/tests/Makefile.am
@@ -33,8 +33,8 @@ AM_CPPFLAGS=$(XAPIAN_CXXFLAGS)						\
 # don't use -Werror, as it might break on other compilers
 # use -Wno-unused-parameters, because some callbacks may not
 # really need all the params they get
-AM_CFLAGS=-Wall -Wextra -Wno-unused-parameter -Wdeclaration-after-statement
-AM_CXXFLAGS=-Wall -Wextra -Wno-unused-parameter
+AM_CFLAGS=${WARN_CFLAGS}
+AM_CXXFLAGS=${WARN_CXXFLAGS}
 
 noinst_PROGRAMS= $(TEST_PROGS)
 
@@ -59,7 +59,7 @@ test_mu_threads_SOURCES= test-mu-threads.c dummy.cc
 test_mu_threads_LDADD=${top_builddir}/lib/tests/libtestmucommon.la
 
 # we need to use dummy.cc to enforce c++ linking...
-BUILT_SOURCES=					\
+BUILT_SOURCES=								\
 	dummy.cc
 dummy.cc:
 	touch dummy.cc
diff --git a/mu/tests/test-mu-cmd-cfind.c b/mu/tests/test-mu-cmd-cfind.c
index 383234db..5231fda0 100644
--- a/mu/tests/test-mu-cmd-cfind.c
+++ b/mu/tests/test-mu-cmd-cfind.c
@@ -98,8 +98,6 @@ test_mu_cfind_bbdb (void)
 {
 	gchar *cmdline, *output, *erroutput, *expected;
 	gchar today[12];
-	const char* frm1;
-	const char *frm2;
 	struct tm *tmtoday;
 	time_t now;
 	const char *old_tz;
@@ -114,24 +112,24 @@ test_mu_cfind_bbdb (void)
 	g_assert (g_spawn_command_line_sync (cmdline, &output, &erroutput,
 					     NULL, NULL));
 
-	frm1 =  ";; -*-coding: utf-8-emacs;-*-\n"
-		";;; file-version: 6\n"
-		"[\"Helmut\" \"Kröger\" nil nil nil nil (\"hk@testmu.xxx\") "
-		"((creation-date . \"%s\") "
+#define frm1   ";; -*-coding: utf-8-emacs;-*-\n"			\
+		";;; file-version: 6\n"					\
+		"[\"Helmut\" \"Kröger\" nil nil nil nil (\"hk@testmu.xxx\") " \
+		"((creation-date . \"%s\") "				\
+		"(time-stamp . \"1970-01-01\")) nil]\n"			\
+		"[\"Mü\" \"\" nil nil nil nil (\"testmu@testmu.xx\") "	\
+		"((creation-date . \"%s\") "				\
 		"(time-stamp . \"1970-01-01\")) nil]\n"
-		"[\"Mü\" \"\" nil nil nil nil (\"testmu@testmu.xx\") "
-		"((creation-date . \"%s\") "
-		"(time-stamp . \"1970-01-01\")) nil]\n";
 
 
-	frm2 =  ";; -*-coding: utf-8-emacs;-*-\n"
-		";;; file-version: 6\n"
-		"[\"Mü\" \"\" nil nil nil nil (\"testmu@testmu.xx\") "
-		"((creation-date . \"%s\") "
+#define	frm2   ";; -*-coding: utf-8-emacs;-*-\n"			\
+		";;; file-version: 6\n"					\
+		"[\"Mü\" \"\" nil nil nil nil (\"testmu@testmu.xx\") "	\
+		"((creation-date . \"%s\") "				\
+		"(time-stamp . \"1970-01-01\")) nil]\n"			\
+		"[\"Helmut\" \"Kröger\" nil nil nil nil (\"hk@testmu.xxx\") " \
+		"((creation-date . \"%s\") "				\
 		"(time-stamp . \"1970-01-01\")) nil]\n"
-		"[\"Helmut\" \"Kröger\" nil nil nil nil (\"hk@testmu.xxx\") "
-		"((creation-date . \"%s\") "
-		"(time-stamp . \"1970-01-01\")) nil]\n";
 
 	g_assert (output);