--- b/lib/libc/gen/pututxline.c	
+++ b/lib/libc/gen/pututxline.c	
@@ -43,26 +43,40 @@ __FBSDID("$FreeBSD$");
 #include "un-namespace.h"
 
 static FILE *
-futx_open(const char *file)
+futx_open(const char *file, const char *lkfile, int *lkfd_out)
 {
 	FILE *fp;
 	struct stat sb;
-	int fd;
+	int fd, lkfd, serrno;
+
+	fd = -1;
+	fp = NULL;
+	serrno = 0;
+
+	lkfd = _open(lkfile, O_CREAT|O_RDWR|O_EXLOCK|O_CLOEXEC, 0600);
+	if (lkfd < 0)
+		return (NULL);
 
 	fd = _open(file, O_CREAT|O_RDWR|O_EXLOCK|O_CLOEXEC, 0644);
 	if (fd < 0)
-		return (NULL);
+		goto out;
 
 	/* Safety check: never use broken files. */
 	if (_fstat(fd, &sb) != -1 && sb.st_size % sizeof(struct futx) != 0) {
-		_close(fd);
-		errno = EFTYPE;
-		return (NULL);
+		serrno = EFTYPE;
+		goto out;
 	}
 
 	fp = fdopen(fd, "r+");
+	*lkfd_out = lkfd;
+out:
 	if (fp == NULL) {
-		_close(fd);
+		if (fd >= 0)
+			_close(fd);
+		if (lkfd >= 0)
+			_close(lkfd);
+		if (serrno != 0)
+			errno = serrno;
 		return (NULL);
 	}
 	return (fp);
@@ -74,7 +88,7 @@ utx_active_add(const struct futx *fu)
 	FILE *fp;
 	struct futx fe;
 	off_t partial;
-	int error, ret;
+	int error, ret, lkfd;
 
 	partial = -1;
 	ret = 0;
@@ -83,7 +97,7 @@ utx_active_add(const struct futx *fu)
 	 * Register user login sessions.  Overwrite entries of sessions
 	 * that have already been terminated.
 	 */
-	fp = futx_open(_PATH_UTX_ACTIVE);
+	fp = futx_open(_PATH_UTX_ACTIVE, _PATH_UTX_ACTIVE_LK, &lkfd);
 	if (fp == NULL)
 		return (-1);
 	while (fread(&fe, sizeof(fe), 1, fp) == 1) {
@@ -133,6 +147,7 @@ utx_active_add(const struct futx *fu)
 	else
 		error = 0;
 	fclose(fp);
+	_close(lkfd);
 	if (error != 0)
 		errno = error;
 	return (error == 0 ? 0 : 1);
@@ -143,12 +158,12 @@ utx_active_remove(struct futx *fu)
 {
 	FILE *fp;
 	struct futx fe;
-	int error, ret;
+	int error, ret, lkfd;
 
 	/*
 	 * Remove user login sessions, having the same ut_id.
 	 */
-	fp = futx_open(_PATH_UTX_ACTIVE);
+	fp = futx_open(_PATH_UTX_ACTIVE, _PATH_UTX_ACTIVE_LK, &lkfd);
 	if (fp == NULL)
 		return (-1);
 	error = ESRCH;
@@ -172,6 +187,7 @@ utx_active_remove(struct futx *fu)
 		}
 
 	fclose(fp);
+	_close(lkfd);
 	if (ret != 0)
 		errno = error;
 	return (ret);
@@ -202,7 +218,7 @@ utx_lastlogin_add(const struct futx *fu)
 {
 	struct futx fe;
 	FILE *fp;
-	int error, ret;
+	int error, ret, lkfd;
 
 	ret = 0;
 
@@ -211,7 +227,7 @@ utx_lastlogin_add(const struct futx *fu)
 	 * current user already has an entry.  If not, append a new
 	 * entry.
 	 */
-	fp = futx_open(_PATH_UTX_LASTLOGIN);
+	fp = futx_open(_PATH_UTX_LASTLOGIN, _PATH_UTX_LASTLOGIN_LK, &lkfd);
 	if (fp == NULL)
 		return (-1);
 	while (fread(&fe, sizeof fe, 1, fp) == 1) {
@@ -229,6 +245,7 @@ utx_lastlogin_add(const struct futx *fu)
 		ret = -1;
 	}
 	fclose(fp);
+	_close(lkfd);
 	if (ret == -1)
 		errno = error;
 	return (ret);
--- b/lib/libc/gen/utxdb.h	
+++ b/lib/libc/gen/utxdb.h	
@@ -34,8 +34,11 @@ 
 #include <stdint.h>
 
 #define	_PATH_UTX_ACTIVE	"/var/run/utx.active"
+#define	_PATH_UTX_ACTIVE_LK	"/var/run/.utx.active.lock"
 #define	_PATH_UTX_LASTLOGIN	"/var/log/utx.lastlogin"
+#define	_PATH_UTX_LASTLOGIN_LK	"/var/log/.utx.lastlogin.lock"
 #define	_PATH_UTX_LOG		"/var/log/utx.log"
+#define	_PATH_UTX_LOG_LK	"/var/log/.utx.log.lock"
 
 /*
  * Entries in struct futx are ordered by how often they are used.  In