diff --git a/lib/libc/regex/regcomp.c b/lib/libc/regex/regcomp.c
--- a/lib/libc/regex/regcomp.c
+++ b/lib/libc/regex/regcomp.c
@@ -828,7 +828,7 @@
 	handled = false;
 
 	assert(MORE());		/* caller should have ensured this */
-	c = GETNEXT();
+	c = (uch)GETNEXT();
 	if (c == '\\') {
 		(void)REQUIRE(MORE(), REG_EESCAPE);
 		cc = GETNEXT();
@@ -1302,7 +1302,7 @@
 
 	if ((p->pflags & PFLAG_LEGACY_ESC) != 0)
 		return (true);
-	if (isalpha(ch) || ch == '\'' || ch == '`')
+	if (iswalpha(ch) || ch == '\'' || ch == '`')
 		return (false);
 	return (true);
 #ifdef NOTYET