diff --git a/fdroidserver/build.py b/fdroidserver/build.py
index 3c37b99b..cd09b5dc 100644
--- a/fdroidserver/build.py
+++ b/fdroidserver/build.py
@@ -118,7 +118,7 @@ def build_server(app, build, vcs, build_dir, output_dir, log_dir, force):
 
         # Helper to copy the contents of a directory to the server...
         def send_dir(path):
-            logging.debug("rsyncing " + path + " to " + ftp.getcwd())
+            logging.debug("rsyncing %s to %s" % (path, ftp.getcwd()))
             # TODO this should move to `vagrant rsync` from >= v1.5
             try:
                 subprocess.check_output(['rsync', '--recursive', '--perms', '--links', '--quiet', '--rsh='