--- a/build/build-clang/build-clang.py
+++ b/build/build-clang/build-clang.py
@@ -77,17 +77,17 @@ def updated_env(env):
 def build_tar_package(tar, name, base, directory):
     name = os.path.realpath(name)
     # On Windows, we have to convert this into an msys path so that tar can
     # understand it.
     if is_windows():
         name = name.replace('\\', '/')
         def f(match):
             return '/' + match.group(1).lower()
-        name = re.sub(r'^([A-Z]):', f, name)
+        name = re.sub(r'^([A-Za-z]):', f, name)
     run_in(base, [tar,
                   "-c",
                   "-%s" % ("J" if ".xz" in name else "j"),
                   "-f",
                   name, directory])
 
 
 def copy_dir_contents(src, dest):