diff --git a/src/Pure/Admin/sync_repos.scala b/src/Pure/Admin/sync_repos.scala
--- a/src/Pure/Admin/sync_repos.scala
+++ b/src/Pure/Admin/sync_repos.scala
@@ -1,101 +1,104 @@
 /*  Title:      Pure/Admin/sync_repos.scala
     Author:     Makarius
 
 Synchronize Isabelle + AFP repositories.
 */
 
 package isabelle
 
 
 object Sync_Repos {
   def sync_repos(context: Rsync.Context, target: String,
     verbose: Boolean = false,
     thorough: Boolean = false,
     preserve_jars: Boolean = false,
     dry_run: Boolean = false,
     rev: String = "",
     afp_root: Option[Path] = None,
     afp_rev: String = ""
   ): Unit = {
     val hg = Mercurial.self_repository()
     val afp_hg = afp_root.map(Mercurial.repository(_))
 
     val more_filter = if (preserve_jars) List("include *.jar", "protect *.jar") else Nil
 
     def sync(hg: Mercurial.Repository, dest: String, r: String,
       contents: List[File.Content] = Nil, filter: List[String] = Nil
     ): Unit = {
       hg.sync(context, dest, rev = r, verbose = verbose, thorough = thorough, dry_run = dry_run,
         contents = contents, filter = filter ::: more_filter)
     }
 
     context.progress.echo_if(verbose, "\n* Isabelle repository:")
     sync(hg, target, rev,
       contents = List(File.Content(Path.explode("etc/ISABELLE_ID"), hg.id(rev = rev))),
       filter = List("protect /AFP"))
 
     for (hg <- afp_hg) {
       context.progress.echo_if(verbose, "\n* AFP repository:")
       sync(hg, Rsync.append(target, "AFP"), afp_rev)
     }
   }
 
   val isabelle_tool =
     Isabelle_Tool("sync_repos", "synchronize Isabelle + AFP repositories",
       Scala_Project.here, { args =>
         var afp_root: Option[Path] = None
         var preserve_jars = false
+        var protect_args = false
         var thorough = false
         var afp_rev = ""
         var dry_run = false
         var rev = ""
         var port = SSH.default_port
         var verbose = false
 
         val getopts = Getopts("""
 Usage: isabelle sync_repos [OPTIONS] TARGET
 
   Options are:
     -A ROOT      include AFP with given root directory (":" for """ + AFP.BASE.implode + """)
     -J           preserve *.jar files
+    -S           robust (but less portable) treatment of spaces in directory names
     -T           thorough treatment of file content and directory times
     -a REV       explicit AFP revision (default: state of working directory)
     -n           no changes: dry-run
     -r REV       explicit revision (default: state of working directory)
     -p PORT      explicit SSH port (default: """ + SSH.default_port + """)
     -v           verbose
 
   Synchronize Isabelle + AFP repositories; see also "isabelle hg_sync".
 
   Example: quick testing
 
     isabelle sync_repos -A: -J testmachine:test/isabelle_afp
 
   Example: accurate testing
 
     isabelle sync_repos -A: -T testmachine:test/isabelle_afp
 """,
           "A:" -> (arg => afp_root = Some(if (arg == ":") AFP.BASE else Path.explode(arg))),
           "J" -> (_ => preserve_jars = true),
+          "S" -> (_ => protect_args = true),
           "T" -> (_ => thorough = true),
           "a:" -> (arg => afp_rev = arg),
           "n" -> (_ => dry_run = true),
           "r:" -> (arg => rev = arg),
           "p:" -> (arg => port = Value.Int.parse(arg)),
           "v" -> (_ => verbose = true))
 
         val more_args = getopts(args)
         val target =
           more_args match {
             case List(target) => target
             case _ => getopts.usage()
           }
 
         val progress = new Console_Progress
-        val context = Rsync.Context(progress, port = port)
+        val context = Rsync.Context(progress, port = port, protect_args = protect_args)
         sync_repos(context, target, verbose = verbose, thorough = thorough,
           preserve_jars = preserve_jars, dry_run = dry_run, rev = rev, afp_root = afp_root,
           afp_rev = afp_rev)
       }
     )
 }