diff --git a/Makefile.am b/Makefile.am
index f809c131..8bfafd40 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -204,6 +204,9 @@ endif
 if NO_IMSG
 nodist_tmux_SOURCES += compat/imsg.c compat/imsg-buffer.c
 endif
+if NO_ERR_H
+nodist_tmux_SOURCES += compat/err.c
+endif
 if NO_CLOSEFROM
 nodist_tmux_SOURCES += compat/closefrom.c
 endif
diff --git a/compat.h b/compat.h
index 47a1706f..5f206120 100644
--- a/compat.h
+++ b/compat.h
@@ -22,6 +22,7 @@
 
 #include <limits.h>
 #include <stdio.h>
+#include <termios.h>
 #include <wchar.h>
 
 #ifndef __GNUC__
@@ -57,6 +58,15 @@ typedef uint32_t u_int32_t;
 typedef uint64_t u_int64_t;
 #endif
 
+#ifdef HAVE_ERR_H
+#include <err.h>
+#else
+void	err(int, const char *, ...);
+void	errx(int, const char *, ...);
+void	warn(const char *, ...);
+void	warnx(const char *, ...);
+#endif
+
 #ifndef HAVE_PATHS_H
 #define	_PATH_BSHELL	"/bin/sh"
 #define	_PATH_TMP	"/tmp/"
diff --git a/compat/cfmakeraw.c b/compat/cfmakeraw.c
index df78ba3f..b481a903 100644
--- a/compat/cfmakeraw.c
+++ b/compat/cfmakeraw.c
@@ -15,7 +15,10 @@
  * OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 
+#include <sys/types.h>
+
 #include <string.h>
+#include <termios.h>
 
 #include "compat.h"
 
diff --git a/compat/err.c b/compat/err.c
new file mode 100644
index 00000000..d7f0c0bd
--- /dev/null
+++ b/compat/err.c
@@ -0,0 +1,97 @@
+/*
+ * Copyright (c) 2017 Nicholas Marriott <nicholas.marriott@gmail.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF MIND, USE, DATA OR PROFITS, WHETHER
+ * IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
+ * OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <sys/types.h>
+
+#include <errno.h>
+#include <stdarg.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+
+#include "compat.h"
+
+void
+err(int eval, const char *fmt, ...)
+{
+	va_list	 ap;
+	int	 saved_errno = errno;
+
+	fprintf(stderr, "%s: ", getprogname());
+
+	va_start(ap, fmt);
+	if (fmt != NULL) {
+		vfprintf(stderr, fmt, ap);
+		fprintf(stderr, ": ");
+	}
+	va_end(ap);
+
+	fprintf(stderr, "%s\n", strerror(saved_errno));
+	exit(eval);
+}
+
+void
+errx(int eval, const char *fmt, ...)
+{
+	va_list	 ap;
+
+	fprintf(stderr, "%s: ", getprogname());
+
+	va_start(ap, fmt);
+	if (fmt != NULL) {
+		vfprintf(stderr, fmt, ap);
+		fprintf(stderr, ": ");
+	}
+	va_end(ap);
+
+	putc('\n', stderr);
+	exit(eval);
+}
+
+void
+warn(const char *fmt, ...)
+{
+	va_list	 ap;
+	int	 saved_errno = errno;
+
+	fprintf(stderr, "%s: ", getprogname());
+
+	va_start(ap, fmt);
+	if (fmt != NULL) {
+		vfprintf(stderr, fmt, ap);
+		fprintf(stderr, ": ");
+	}
+	va_end(ap);
+
+	fprintf(stderr, "%s\n", strerror(saved_errno));
+}
+
+void
+warnx(const char *fmt, ...)
+{
+	va_list	 ap;
+
+	fprintf(stderr, "%s: ", getprogname());
+
+	va_start(ap, fmt);
+	if (fmt != NULL) {
+		vfprintf(stderr, fmt, ap);
+		fprintf(stderr, ": ");
+	}
+	va_end(ap);
+
+	putc('\n', stderr);
+}
diff --git a/compat/forkpty-sunos.c b/compat/forkpty-sunos.c
index 0de36bf5..81109630 100644
--- a/compat/forkpty-sunos.c
+++ b/compat/forkpty-sunos.c
@@ -21,6 +21,7 @@
 #include <stdlib.h>
 #include <strings.h>
 #include <stropts.h>
+#include <termios.h>
 #include <unistd.h>
 
 #include "compat.h"
diff --git a/configure.ac b/configure.ac
index acfc5886..79dfcb31 100644
--- a/configure.ac
+++ b/configure.ac
@@ -350,6 +350,16 @@ if test "x$found_cmsg_data" = xno; then
 fi
 AC_SUBST(XOPEN_DEFINES)
 
+# Look for err and friends in err.h.
+AC_CHECK_FUNC(err, found_err_h=yes, found_err_h=no)
+AC_CHECK_FUNC(errx, , found_err_h=no)
+AC_CHECK_FUNC(warn, , found_err_h=no)
+AC_CHECK_FUNC(warnx, , found_err_h=no)
+if test "x$found_err_h" = xyes; then
+	AC_CHECK_HEADER(err.h, , found_err_h=no)
+fi
+AM_CONDITIONAL(NO_ERR_H, [test "x$found_err_h" = xno])
+
 # Look for imsg in libutil. compat/imsg.c is linked by Makefile.am if missing.
 AC_SEARCH_LIBS(imsg_init, util, found_imsg_init=yes, found_imsg_init=no)
 if test "x$found_imsg_init" = xyes; then
diff --git a/tmux.c b/tmux.c
index c9ae92ef..b9809568 100644
--- a/tmux.c
+++ b/tmux.c
@@ -19,7 +19,6 @@
 #include <sys/types.h>
 #include <sys/stat.h>
 
-#include <err.h>
 #include <errno.h>
 #include <event.h>
 #include <fcntl.h>
diff --git a/tmux.h b/tmux.h
index 3d25898c..ded5dfc9 100644
--- a/tmux.h
+++ b/tmux.h
@@ -55,7 +55,9 @@ struct tmuxpeer;
 struct tmuxproc;
 
 /* Default global configuration file. */
+#ifndef TMUX_CONF
 #define TMUX_CONF "/etc/tmux.conf"
+#endif
 
 /*
  * Minimum layout cell size, NOT including separator line. The scroll region