diff --git a/usr.sbin/pw/edgroup.c b/usr.sbin/pw/edgroup.c
index c927b06cc30a..6116fa6854ac 100644
--- a/usr.sbin/pw/edgroup.c
+++ b/usr.sbin/pw/edgroup.c
@@ -26,7 +26,7 @@
 
 #ifndef lint
 static const char rcsid[] =
-	"$Id$";
+	"$Id: edgroup.c,v 1.5 1997/10/10 06:23:30 charnier Exp $";
 #endif /* not lint */
 
 #include <stdio.h>
@@ -64,7 +64,7 @@ editgroups(char *name, char **groups)
 	int             rc = 0;
 	int             infd;
 
-	if ((infd = open(groupfile, O_RDWR | O_CREAT | O_EXLOCK, 0644)) != -1) {
+	if ((infd = open(groupfile, O_RDWR | O_CREAT, 0644)) != -1) {
 		FILE           *infp;
 
 		if ((infp = fdopen(infd, "r+")) == NULL)
diff --git a/usr.sbin/pw/fileupd.c b/usr.sbin/pw/fileupd.c
index 3782bf7d1da4..fe46480048d1 100644
--- a/usr.sbin/pw/fileupd.c
+++ b/usr.sbin/pw/fileupd.c
@@ -26,7 +26,7 @@
 
 #ifndef lint
 static const char rcsid[] =
-	"$Id$";
+	"$Id: fileupd.c,v 1.5 1997/10/10 06:23:31 charnier Exp $";
 #endif /* not lint */
 
 #include <stdio.h>
@@ -76,7 +76,7 @@ fileupdate(char const * filename, mode_t fmode, char const * newline, char const
 	if (pfxlen <= 1)
 		errno = EINVAL;
 	else {
-		int             infd = open(filename, O_RDWR | O_CREAT | O_EXLOCK, fmode);
+		int             infd = open(filename, O_RDWR | O_CREAT, fmode);
 
 		if (infd != -1) {
 			FILE           *infp = fdopen(infd, "r+");
@@ -168,9 +168,20 @@ fileupdate(char const * filename, mode_t fmode, char const * newline, char const
 									fputs(line, infp);
 
 								/*
+                                                                 * If there was a problem with copying
+                                                                 * we will just rename 'file.new' 
+                                                                 * to 'file'.
 								 * This is a gross hack, but we may have
 								 * corrupted the original file
-								 * Unfortunately, it will lose the inode.
+								 * Unfortunately, it will lose the inode
+                                                                 * and hence the lock.
+                                                                 *
+                                                                 * The implications of this is that this invocation of pw 
+                                                                 * won't have the file locked and concurrent copies
+                                                                 * of pw, vipw etc could clobber what this one is doing.
+                                                                 *
+                                                                 * It should probably just return an error instead
+                                                                 * of going on like nothing is wrong.
 								 */
 								if (fflush(infp) == EOF || ferror(infp))
 									rc = rename(file, filename) == 0;
diff --git a/usr.sbin/pw/pw.c b/usr.sbin/pw/pw.c
index 634716e5208d..5daa213c880b 100644
--- a/usr.sbin/pw/pw.c
+++ b/usr.sbin/pw/pw.c
@@ -26,11 +26,12 @@
 
 #ifndef lint
 static const char rcsid[] =
-	"$Id$";
+	"$Id: pw.c,v 1.7 1997/10/10 06:23:34 charnier Exp $";
 #endif /* not lint */
 
 #include "pw.h"
 #include <err.h>
+#include <fcntl.h>
 #include <paths.h>
 #include <sys/wait.h>
 
@@ -49,6 +50,7 @@ static struct cargs arglist;
 
 static int      getindex(const char *words[], const char *word);
 static void     cmdhelp(int mode, int which);
+static int      filelock(const char *filename);
 
 
 int
@@ -147,7 +149,20 @@ main(int argc, char *argv[])
 	 * Now, let's do the common initialisation
 	 */
 	cnf = read_userconfig(getarg(&arglist, 'C') ? getarg(&arglist, 'C')->val : NULL);
-	ch = funcs[which] (cnf, mode, &arglist);
+
+
+	/*
+	 * Be pessimistic and lock the master passowrd and group
+	 * files right away.  Keep it locked for the duration.
+	 */
+	if (-1 == filelock(_PATH_GROUP) || -1 == filelock(_PATH_MASTERPASSWD))
+	{
+		ch = EX_IOERR;
+	}
+	else
+	{
+		ch = funcs[which] (cnf, mode, &arglist);
+	}	
 
 	/*
 	 * If everything went ok, and we've been asked to update
@@ -177,6 +192,12 @@ main(int argc, char *argv[])
 	return ch;
 }
 
+static int
+filelock(const char *filename)
+{
+	return open(filename, O_RDONLY | O_EXLOCK, 0);
+}
+
 static int
 getindex(const char *words[], const char *word)
 {