diff --git a/src/url.lua b/src/url.lua
index 1e5a3f6..d61111e 100644
--- a/src/url.lua
+++ b/src/url.lua
@@ -49,7 +49,7 @@ local function make_set(t)
     return s
 end
 
--- these are allowed withing a path segment, along with alphanum
+-- these are allowed within a path segment, along with alphanum
 -- other characters must be escaped
 local segment_set = make_set {
     "-", "_", ".", "!", "~", "*", "'", "(",
@@ -59,7 +59,7 @@ local segment_set = make_set {
 local function protect_segment(s)
     return string.gsub(s, "([^A-Za-z0-9_])", function (c)
         if segment_set[c] then return c
-        else return string.format("%%%02x", string.byte(c)) end
+        else return string.format("%%%02X", string.byte(c)) end
     end)
 end