diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index ccb664b..be0e7cf 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -1324,7 +1324,10 @@
 	}
 
 	for (i = 0; i < 16; i++) {
-		p = hex_byte_pack(p, addr[index[i]]);
+		if (uc)
+			p = hex_byte_pack_upper(p, addr[index[i]]);
+		else
+			p = hex_byte_pack(p, addr[index[i]]);
 		switch (i) {
 		case 3:
 		case 5:
@@ -1337,13 +1340,6 @@
 
 	*p = 0;
 
-	if (uc) {
-		p = uuid;
-		do {
-			*p = toupper(*p);
-		} while (*(++p));
-	}
-
 	return string(buf, end, uuid, spec);
 }