diff --git a/Makefile.am b/Makefile.am
index 7ac3d6ac..59ba9187 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -16,6 +16,9 @@ AM_CPPFLAGS += @XOPEN_DEFINES@ -DTMUX_CONF="\"$(sysconfdir)/tmux.conf\""
 # Additional object files.
 LDADD = $(LIBOBJS)
 
+# Add math for sixel
+AM_LDFLAGS = -lm
+
 # Set flags for gcc.
 if IS_GCC
 AM_CFLAGS += -std=gnu99 -O2
diff --git a/configure.ac b/configure.ac
index 5fba1eaf..0712c265 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1,7 +1,8 @@
 # configure.ac
 
-AC_INIT([tmux], next-3.1)
-AC_PREREQ([2.60])
+AC_INIT([tmux],[next-3.1])
+AC_PREREQ([2.71])
+AC_CONFIG_FILES([Makefile])
 
 AC_CONFIG_AUX_DIR(etc)
 AC_CONFIG_LIBOBJ_DIR(compat)
@@ -23,8 +24,6 @@ SAVED_LDFLAGS="$LDFLAGS"
 
 # Set up the compiler in two different ways and say yes we may want to install.
 AC_PROG_CC
-AM_PROG_CC_C_O
-AC_PROG_CC_C99
 AC_PROG_CPP
 AC_PROG_EGREP
 AC_PROG_INSTALL
@@ -39,14 +38,14 @@ test "$sysconfdir" = '${prefix}/etc' && sysconfdir=/etc
 case "x$VERSION" in xnext*) enable_debug=yes;; esac
 AC_ARG_ENABLE(
 	debug,
-	AC_HELP_STRING(--enable-debug, enable debug build flags),
+	AS_HELP_STRING(--enable-debug, enable debug build flags),
 )
 AM_CONDITIONAL(IS_DEBUG, test "x$enable_debug" = xyes)
 
 # Is this a static build?
 AC_ARG_ENABLE(
 	static,
-	AC_HELP_STRING(--enable-static, create a static build)
+	AS_HELP_STRING(--enable-static, create a static build)
 )
 if test "x$enable_static" = xyes; then
 	test "x$PKG_CONFIG" != x && PKG_CONFIG="$PKG_CONFIG --static"
@@ -228,7 +227,7 @@ fi
 # Look for utempter.
 AC_ARG_ENABLE(
 	utempter,
-	AC_HELP_STRING(--enable-utempter, use utempter if it is installed)
+	AS_HELP_STRING(--enable-utempter, use utempter if it is installed)
 )
 if test "x$enable_utempter" = xyes; then
 	AC_CHECK_HEADER(utempter.h, enable_utempter=yes, enable_utempter=no)
@@ -250,7 +249,7 @@ fi
 # Look for utf8proc.
 AC_ARG_ENABLE(
 	utf8proc,
-	AC_HELP_STRING(--enable-utf8proc, use utf8proc if it is installed)
+	AS_HELP_STRING(--enable-utf8proc, use utf8proc if it is installed)
 )
 if test "x$enable_utf8proc" = xyes; then
 	AC_CHECK_HEADER(utf8proc.h, enable_utf8proc=yes, enable_utf8proc=no)
@@ -272,32 +271,24 @@ AM_CONDITIONAL(HAVE_UTF8PROC, [test "x$enable_utf8proc" = xyes])
 
 # Check for b64_ntop. If we have b64_ntop, we assume b64_pton as well.
 AC_MSG_CHECKING(for b64_ntop)
-AC_TRY_LINK(
-	[
+AC_LINK_IFELSE([AC_LANG_PROGRAM([[
 		#include <sys/types.h>
 		#include <netinet/in.h>
 		#include <resolv.h>
-	],
-	[b64_ntop(NULL, 0, NULL, 0);],
-	found_b64_ntop=yes,
-	found_b64_ntop=no
-)
+	]], [[b64_ntop(NULL, 0, NULL, 0);]])],[found_b64_ntop=yes],[found_b64_ntop=no
+])
 if test "x$found_b64_ntop" = xno; then
 	AC_MSG_RESULT(no)
 
 	AC_MSG_CHECKING(for b64_ntop with -lresolv)
 	OLD_LIBS="$LIBS"
 	LIBS="$LIBS -lresolv"
-	AC_TRY_LINK(
-		[
+	AC_LINK_IFELSE([AC_LANG_PROGRAM([[
 			#include <sys/types.h>
 			#include <netinet/in.h>
 			#include <resolv.h>
-		],
-		[b64_ntop(NULL, 0, NULL, 0);],
-		found_b64_ntop=yes,
-		found_b64_ntop=no
-	)
+		]], [[b64_ntop(NULL, 0, NULL, 0);]])],[found_b64_ntop=yes],[found_b64_ntop=no
+	])
 	if test "x$found_b64_ntop" = xno; then
 		LIBS="$OLD_LIBS"
 		AC_MSG_RESULT(no)
@@ -652,4 +643,4 @@ AC_SUBST(AM_LDFLAGS)
 LDFLAGS="$SAVED_LDFLAGS"
 
 # autoconf should create a Makefile.
-AC_OUTPUT(Makefile)
+AC_OUTPUT
diff --git a/tmux.c b/tmux.c
index 244e2d35..a26cb4d1 100644
--- a/tmux.c
+++ b/tmux.c
@@ -141,7 +141,7 @@ make_label(const char *label, char **cause)
 #if __MSYS__ || __CYGWIN__ || _WIN32 || _WIN64
         if (sb.st_uid != uid) {
 #else
-        if (sb.st_uid != uid || (sb.st_mode & PERMS) != 0) {
+        if (sb.st_uid != uid || (sb.st_mode & ACCESSPERMS) != 0) {
 #endif
 		errno = EACCES;
 		goto fail;