diff --git a/README.md b/README.md
index 0c8987c..e13d55b 100644
--- a/README.md
+++ b/README.md
@@ -374,7 +374,7 @@ import re
 def immutable_file_test(path, url):
     # Match filename with 12 hex digits before the extension
     # e.g. app.db8f2edc0c8a.js
-    return re.match(r"^.+\.[0-9a-f]{8,12}\..+$", url)
+    return re.match(r"^.+[\.\-][0-9a-f]{8,12}\..+$", url)
 
 
 WHITENOISE_IMMUTABLE_FILE_TEST = immutable_file_test