diff --git a/lib/libc/locale/collate.c b/lib/libc/locale/collate.c
--- a/lib/libc/locale/collate.c
+++ b/lib/libc/locale/collate.c
@@ -300,7 +300,7 @@
 	while (low <= high) {
 		next = (low + high) / 2;
 		p = tab + next;
-		compar = key - p->val;
+		compar = (uint32_t)key - p->val;
 		if (compar == 0)
 			return (p);
 		if (compar > 0)
@@ -359,7 +359,7 @@
 		*len = l;
 		*pri = p;
 
-	} else if (*t <= UCHAR_MAX) {
+	} else if (*t >= 0 && *t <= UCHAR_MAX) {
 
 		/*
 		 * Character is a small (8-bit) character.
@@ -699,12 +699,17 @@
 	struct xlocale_collate *table =
 		(struct xlocale_collate*)locale->components[XLC_COLLATE];
 
-	if (table->__collate_load_error)
-		return ((len == 1 && *str <= UCHAR_MAX) ? *str : -1);
+	if (table->__collate_load_error) {
+		if (len != 1)
+			return (-1);
+		if (*str < 0 || *str > UCHAR_MAX)
+			return (-1);
+		return (*str);
+	}
 
 	if (len == 1) {
 		e = -1;
-		if (*str <= UCHAR_MAX)
+		if (*str >= 0 && *str <= UCHAR_MAX)
 			e = table->char_pri_table[*str].pri[0];
 		else if (table->info->large_count > 0) {
 			collate_large_t *match_large;
@@ -781,7 +786,7 @@
 	if (len == 0 || len > dlen)
 		return ((size_t)-1);
 	if (len == 1) {
-		if (*wname <= UCHAR_MAX) {
+		if (*wname >= 0 && *wname <= UCHAR_MAX) {
 			if (table->char_pri_table[*wname].pri[0] >= 0) {
 				if (dlen > 0)
 					*dst = *wname;
@@ -853,7 +858,7 @@
 		return (-1);
 	if (len == 1) {
 		e = -1;
-		if (*wname <= UCHAR_MAX)
+		if (*wname >= 0 && *wname <= UCHAR_MAX)
 			e = table->char_pri_table[*wname].pri[0];
 		else if (table->info->large_count > 0) {
 			collate_large_t *match;
@@ -946,7 +951,7 @@
 	}
 	/* try single character */
 	i = 1;
-	if (*buf <= UCHAR_MAX) {
+	if (*buf >= 0 && *buf <= UCHAR_MAX) {
 		if (equiv_class == table->char_pri_table[*buf].pri[0])
 			goto found;
 	} else if (table->info->large_count > 0) {