Index: contrib/libc-vis/vis.c
===================================================================
--- contrib/libc-vis/vis.c	(revision 271241)
+++ contrib/libc-vis/vis.c	(working copy)
@@ -105,6 +105,7 @@
 #define XTOA(c)		L"0123456789ABCDEF"[c]
 
 #define MAXEXTRAS	10
+#define MB_STRZ		(-1)
 
 #if !HAVE_NBTOOL_CONFIG_H
 #ifndef __NetBSD__
@@ -345,7 +346,7 @@
  *	All user-visible functions call this one.
  */
 static int
-istrsenvisx(char *mbdst, size_t *dlen, const char *mbsrc, size_t mblength,
+istrsenvisx(char *mbdst, size_t *dlen, const char *mbsrc, ssize_t mblength,
     int flags, const char *mbextra, int *cerr_ptr)
 {
 	wchar_t *dst, *src, *pdst, *psrc, *start, *extra;
@@ -357,8 +358,9 @@
 	ssize_t mbslength, maxolen;
 
 	_DIAGASSERT(mbdst != NULL);
-	_DIAGASSERT(mbsrc != NULL);
+	_DIAGASSERT(mbsrc != NULL || mblength == 0);
 	_DIAGASSERT(mbextra != NULL);
+	_DIAGASSERT(mblength >= 0 || mblength == MB_STRZ);
 
 	/*
 	 * Input (mbsrc) is a char string considered to be multibyte
@@ -375,7 +377,7 @@
 
 	/* Allocate space for the wide char strings */
 	psrc = pdst = extra = NULL;
-	if (!mblength)
+	if (mblength == MB_STRZ)
 		mblength = strlen(mbsrc);
 	if ((psrc = calloc(mblength + 1, sizeof(*psrc))) == NULL)
 		return -1;
@@ -394,7 +396,7 @@
 	 * stop at NULs because we may be processing a block of data
 	 * that includes NULs.
 	 */
-	mbslength = (ssize_t)mblength;
+	mbslength = mblength;
 	/*
 	 * When inputing a single character, must also read in the
 	 * next character for nextc, the look-ahead character.
@@ -431,7 +433,7 @@
 	 * processed two characters, c and nextc.  Reset len back to
 	 * just a single character.
 	 */
-	if (mblength < len)
+	if ((size_t)mblength < len)
 		len = mblength;
 
 	/* Convert extra argument to list of characters for this mode. */
@@ -571,13 +573,13 @@
 int
 strsvis(char *mbdst, const char *mbsrc, int flags, const char *mbextra)
 {
-	return istrsenvisx(mbdst, NULL, mbsrc, 0, flags, mbextra, NULL);
+	return istrsenvisx(mbdst, NULL, mbsrc, MB_STRZ, flags, mbextra, NULL);
 }
 
 int
 strsnvis(char *mbdst, size_t dlen, const char *mbsrc, int flags, const char *mbextra)
 {
-	return istrsenvisx(mbdst, &dlen, mbsrc, 0, flags, mbextra, NULL);
+	return istrsenvisx(mbdst, &dlen, mbsrc, MB_STRZ, flags, mbextra, NULL);
 }
 
 int
@@ -646,13 +648,13 @@
 int
 strvis(char *mbdst, const char *mbsrc, int flags)
 {
-	return istrsenvisx(mbdst, NULL, mbsrc, 0, flags, "", NULL);
+	return istrsenvisx(mbdst, NULL, mbsrc, MB_STRZ, flags, "", NULL);
 }
 
 int
 strnvis(char *mbdst, size_t dlen, const char *mbsrc, int flags)
 {
-	return istrsenvisx(mbdst, &dlen, mbsrc, 0, flags, "", NULL);
+	return istrsenvisx(mbdst, &dlen, mbsrc, MB_STRZ, flags, "", NULL);
 }
 
 /*