diff --git a/include/string.h b/include/string.h
index 66b14f4fac23..5f2a6e128cd0 100644
--- a/include/string.h
+++ b/include/string.h
@@ -62,6 +62,7 @@ int	 strcoll __P((const char *, const char *));
 char	*strcpy __P((char *, const char *));
 size_t	 strcspn __P((const char *, const char *));
 char	*strerror __P((int));
+int	 strerror_r __P((int, char *, size_t));
 size_t	 strlen __P((const char *));
 char	*strncat __P((char *, const char *, size_t));
 int	 strncmp __P((const char *, const char *, size_t));
diff --git a/lib/libc/string/strerror.3 b/lib/libc/string/strerror.3
index 447e208c39c0..ed63b25f5be7 100644
--- a/lib/libc/string/strerror.3
+++ b/lib/libc/string/strerror.3
@@ -36,12 +36,13 @@
 .\"     @(#)strerror.3	8.1 (Berkeley) 6/9/93
 .\" $FreeBSD$
 .\"
-.Dd June 9, 1993
+.Dd Nov 26, 2001
 .Dt STRERROR 3
 .Os
 .Sh NAME
 .Nm perror ,
 .Nm strerror ,
+.Nm strerror_r ,
 .Nm sys_errlist ,
 .Nm sys_nerr
 .Nd system error messages
@@ -56,9 +57,12 @@
 .In string.h
 .Ft char *
 .Fn strerror "int errnum"
+.Ft int
+.Fn strerror_r "int errnum" "char * strerrbuf" "size_t buflen"
 .Sh DESCRIPTION
 The
-.Fn strerror
+.Fn strerror ,
+.Fn strerror_r 
 and
 .Fn perror
 functions look up the error message string corresponding to an
@@ -68,11 +72,27 @@ The
 .Fn strerror
 function accepts an error number argument
 .Fa errnum
-and
-returns a pointer to the corresponding
+and returns a pointer to the corresponding
 message string.
 .Pp
 The
+.Fn strerror_r
+function renders the same result into
+.Fa strerrbuf
+for a maximum of 
+.Fa buflen
+characters and returns 0 upon success.  If insufficient
+storage is provided in
+.Fa strerrbuf 
+(as specified in 
+.Fa buflen )
+to contain the error string, 
+.Er ERANGE 
+is returned and the string in 
+.Fa strerrbuf
+may not be null-terminated.
+.Pp
+The
 .Fn perror
 function finds the error message corresponding to the current
 value of the global variable
@@ -107,6 +127,8 @@ contains a count of the messages in
 .Va sys_errlist .
 The use of these variables is deprecated;
 .Fn strerror
+or
+.Fn strerror_r
 should be used instead.
 .Sh SEE ALSO
 .Xr intro 2 ,
@@ -118,6 +140,13 @@ and
 .Fn perror
 functions first appeared in
 .Bx 4.4 .
+The 
+.Fn strerror_r
+function was implemented in
+.Fx 4.4
+by 
+.An Wes Peters
+.Aq wes@freebsd.org .
 .Sh BUGS
 For unknown error numbers, the
 .Fn strerror
diff --git a/lib/libc/string/strerror.c b/lib/libc/string/strerror.c
index 626e5d7287a7..8628d8d9c436 100644
--- a/lib/libc/string/strerror.c
+++ b/lib/libc/string/strerror.c
@@ -39,35 +39,90 @@ __FBSDID("$FreeBSD$");
 
 #include <stdio.h>
 #include <string.h>
+#include <errno.h>
+
+
+int
+strerror_r(int errnum, char *strerrbuf, size_t buflen)
+{
+#define	UPREFIX	"Unknown error: "
+	unsigned int uerr;
+	char *p, *t;
+	char tmp[40];				/* 64-bit number + slop */
+	int len;
+
+	uerr = errnum;				/* convert to unsigned */
+	if (uerr < sys_nerr) {
+		len = strlcpy(strerrbuf, (char *)sys_errlist[uerr], buflen);
+		return (len <= buflen) ? 0 : ERANGE;
+	}
+
+	/* Print unknown errno by hand so we don't link to stdio(3). */
+	t = tmp;
+	if (errnum < 0)
+		uerr = -uerr;
+	do {
+		*t++ = "0123456789"[uerr % 10];
+	} while (uerr /= 10);
+
+	if (errnum < 0)
+		*t++ = '-';
+
+	strlcpy(strerrbuf, UPREFIX, buflen);
+	for (p = strerrbuf + sizeof(UPREFIX) - 1; p < strerrbuf + buflen; ) {
+		*p++ = *--t;
+		if (t <= tmp)
+			break;
+	}
+
+	if (p < strerrbuf + buflen) {
+		*p = '\0';
+		return 0;
+	}
+
+	return ERANGE;
+}
+
+
+/*
+ * NOTE: the following length should be enough to hold the longest defined
+ * error message in sys_errlist, defined in ../gen/errlst.c.  This is a WAG
+ * that is better than the previous value.
+ */
+#define ERR_LEN 64
 
 char *
 strerror(num)
 	int num;
 {
-#define	UPREFIX	"Unknown error: "
-	static char ebuf[40] = UPREFIX;		/* 64-bit number + slop */
-	register unsigned int errnum;
-	register char *p, *t;
-	char tmp[40];
+	unsigned int uerr;
+	static char ebuf[ERR_LEN];
 
-	errnum = num;				/* convert to unsigned */
-	if (errnum < sys_nerr)
-		return ((char *)sys_errlist[errnum]);
+	uerr = num;				/* convert to unsigned */
+	if (uerr < sys_nerr)
+		return (char *)sys_errlist[uerr];
 
-	/* Do this by hand, so we don't link to stdio(3). */
-	t = tmp;
-	if (num < 0)
-		errnum = -errnum;
-	do {
-		*t++ = "0123456789"[errnum % 10];
-	} while (errnum /= 10);
-	if (num < 0)
-		*t++ = '-';
-	for (p = ebuf + sizeof(UPREFIX) - 1;;) {
-		*p++ = *--t;
-		if (t <= tmp)
-			break;
-	}
-	*p = '\0';
-	return (ebuf);
+	/* strerror can't fail so handle truncation semi-elegantly */
+	if (strerror_r(num, ebuf, (size_t) ERR_LEN) != 0)
+	    ebuf[ERR_LEN - 1] = '\0';
+
+	return ebuf;
 }
+
+
+#ifdef STANDALONE_TEST
+main()
+{
+	char mybuf[64];
+	int ret;
+
+	printf("strerror(47) yeilds: %s\n", strerror(47));
+	strerror_r(11, mybuf, 64);
+	printf("strerror_r(11) yeilds: %s\n", mybuf);
+	strerror_r(1234, mybuf, 64);
+	printf("strerror_r(1234) yeilds: %s\n", mybuf);
+	memset(mybuf, '*', 63);
+	ret = strerror_r(4321, mybuf, 16);
+	printf("strerror_r on short buffer returns %d (%s)\n", ret, mybuf);
+}
+#endif