--- a/src/Pure/System/isabelle_system.scala
+++ b/src/Pure/System/isabelle_system.scala
@@ -214,6 +214,7 @@ object Isabelle_System {
         Files.copy(src.toPath, target.toPath,
           StandardCopyOption.COPY_ATTRIBUTES,
           StandardCopyOption.REPLACE_EXISTING)
+        target.setWritable(true)
       }
       catch {
         case ERROR(msg) =>