diff --git a/lib/sprockets/server.rb b/lib/sprockets/server.rb
index c32ce2228..fadfd6fc1 100644
--- a/lib/sprockets/server.rb
+++ b/lib/sprockets/server.rb
@@ -309,7 +309,7 @@ def headers(env, asset, length)
       #     # => "0aa2105d29558f3eb790d411d7d8fb66"
       #
       def path_fingerprint(path)
-        path[/-([0-9a-zA-Z]{7,128})\.[^.]+\z/, 1]
+        path[/-([0-9a-f]{7,128})\.[^.]+\z/, 1]
       end
   end
 end