--- zabbix-4.0.0+dfsg.orig/m4/iconv.m4
+++ zabbix-4.0.0+dfsg/m4/iconv.m4
@@ -69,7 +69,8 @@
 
 	AC_MSG_CHECKING(for ICONV support)
 
-	if test -n "$_iconv_dir_set" -o -f /usr/include/iconv.h; then
+	AC_CHECK_HEADER([iconv.h],[found_iconv=yes])
+	if test -n "$_iconv_dir_set" -o "x$found_iconv" = xyes; then
 		found_iconv="yes"
 	elif test -f /usr/local/include/iconv.h; then
 		ICONV_CFLAGS="-I/usr/local/include"
--- zabbix-4.0.0+dfsg.orig/m4/pthread.m4
+++ zabbix-4.0.0+dfsg/m4/pthread.m4
@@ -105,7 +105,8 @@
 
 	LIBPTHREAD_LIBS="-lpthread"
 
-	if test -n "$_libpthread_dir_set" -o -f /usr/include/pthread.h; then
+	AC_CHECK_HEADER([pthread.h],[found_libpthread=yes])
+	if test -n "$_libpthread_dir_set" -o "x$found_libpthread" = xyes; then
 		found_libpthread="yes"
 	elif test -f /usr/local/include/pthread.h; then
 		LIBPTHREAD_CFLAGS="-I/usr/local/include"