diff --git a/util/mode.c b/util/mode.c
index 4506023..c022e8d 100644
--- a/util/mode.c
+++ b/util/mode.c
@@ -16,9 +16,9 @@ mode_t
 parsemode(const char *str, mode_t mode, mode_t mask)
 {
 	char *end;
-	const char *p;
-	int octal, op = '+';
-	mode_t gmask = 0, m = 0;
+	const char *p = str;
+	int octal, op;
+	mode_t who, perm, clear;
 
 	octal = strtol(str, &end, 8);
 	if(*end == '\0') {
@@ -41,61 +41,122 @@ parsemode(const char *str, mode_t mode, mode_t mask)
 		if(octal & 00001) mode |= S_IXOTH;
 		return mode;
 	}
-	for(p = str; *p; p++) {
+next:
+	/* first, determine which bits we will be modifying */
+	for(who = 0; *p; p++) {
 		switch(*p) {
 		/* masks */
 		case 'u':
-			gmask |= S_IRWXU;
-			break;
+			who |= S_IRWXU|S_ISUID;
+			continue;
 		case 'g':
-			gmask |= S_IRWXG;
-			break;
+			who |= S_IRWXG|S_ISGID;
+			continue;
 		case 'o':
-			gmask |= S_IRWXO;
-			break;
+			who |= S_IRWXO;
+			continue;
 		case 'a':
-			gmask |= S_IRWXU|S_IRWXG|S_IRWXO;
-			break;
+			who |= S_IRWXU|S_ISUID|S_IRWXG|S_ISGID|S_IRWXO;
+			continue;
+		}
+		break;
+	}
+	if(who) {
+		clear = who;
+	} else {
+		clear = S_ISUID|S_ISGID|S_ISVTX|S_IRWXU|S_IRWXG|S_IRWXO;
+		who = ~mask;
+	}
+	while(*p) {
+		switch(*p) {
 		/* opers */
 		case '=':
 		case '+':
 		case '-':
 			op = (int)*p;
 			break;
-		/* modes */
-		case 'r':
-			m |= S_IRUSR|S_IRGRP|S_IROTH;
-			break;
-		case 'w':
-			m |= S_IWUSR|S_IWGRP|S_IWOTH;
-			break;
-		case 'x':
-			m |= S_IXUSR|S_IXGRP|S_IXOTH;
-			break;
-		case 's':
-			m |= S_ISUID|S_ISGID;
-			break;
-		case 't':
-			m |= S_ISVTX;
-			break;
 		default:
 			eprintf("%s: invalid mode\n", str);
 			return -1;
 		}
+
+		perm = 0;
+		switch(*++p) {
+		/* copy */
+		case 'u':
+			if(mode & S_IRUSR)
+					perm |= S_IRUSR|S_IRGRP|S_IROTH;
+			if(mode & S_IWUSR)
+					perm |= S_IWUSR|S_IWGRP|S_IWOTH;
+			if(mode & S_IXUSR)
+					perm |= S_IXUSR|S_IXGRP|S_IXOTH;
+			if(mode & S_ISUID)
+					perm |= S_ISUID|S_ISGID;
+			p++;
+			break;
+		case 'g':
+			if(mode & S_IRGRP)
+					perm |= S_IRUSR|S_IRGRP|S_IROTH;
+			if(mode & S_IWGRP)
+					perm |= S_IWUSR|S_IWGRP|S_IWOTH;
+			if(mode & S_IXGRP)
+					perm |= S_IXUSR|S_IXGRP|S_IXOTH;
+			if(mode & S_ISGID)
+					perm |= S_ISUID|S_ISGID;
+			p++;
+			break;
+		case 'o':
+			if(mode & S_IROTH)
+					perm |= S_IRUSR|S_IRGRP|S_IROTH;
+			if(mode & S_IWOTH)
+					perm |= S_IWUSR|S_IWGRP|S_IWOTH;
+			if(mode & S_IXOTH)
+					perm |= S_IXUSR|S_IXGRP|S_IXOTH;
+			p++;
+			break;
+		default:
+			for(; *p; p++) {
+				switch(*p) {
+				/* modes */
+				case 'r':
+					perm |= S_IRUSR|S_IRGRP|S_IROTH;
+					break;
+				case 'w':
+					perm |= S_IWUSR|S_IWGRP|S_IWOTH;
+					break;
+				case 'x':
+					perm |= S_IXUSR|S_IXGRP|S_IXOTH;
+					break;
+				case 's':
+					perm |= S_ISUID|S_ISGID;
+					break;
+				case 't':
+					perm |= S_ISVTX;
+					break;
+				default:
+					goto apply;
+				}
+			}
+		}
+
+	apply:
 		/* apply */
 		switch(op) {
+		case '=':
+			mode &= ~clear;
+			/* fallthrough */
 		case '+':
-			mode |= (m & ((~mask) & 0777));
+			mode |= perm & who;
 			break;
 		case '-':
-			mode &= (~(m & ((~mask) & 0777)));
-			break;
-		case '=':
-			mode = (m & ((~mask) & 0777));
+			mode &= ~(perm & who);
 			break;
 		}
+		/* if we hit a comma, move on to the next clause */
+		if(*p == ',') {
+			p++;
+			goto next;
+		}
 	}
-	if(gmask && op != '=')
-		mode &= ~gmask;
 	return mode;
 }