diff --git a/gc.c b/gc.c
index 4ffe0301..550c1db4 100644
--- a/gc.c
+++ b/gc.c
@@ -485,6 +485,7 @@ char *gc_copy_obj(object dest, char *obj, gc_thread_data * thd)
       type_of(hp) = port_tag;
       hp->fp = ((port_type *) obj)->fp;
       hp->mode = ((port_type *) obj)->mode;
+      hp->flags = ((port_type *) obj)->flags;
       hp->mem_buf = ((port_type *)obj)->mem_buf;
       hp->mem_buf_len = ((port_type *)obj)->mem_buf_len;
       return (char *)hp;
diff --git a/include/cyclone/types.h b/include/cyclone/types.h
index 0da9c00d..20c45761 100644
--- a/include/cyclone/types.h
+++ b/include/cyclone/types.h
@@ -778,6 +778,7 @@ typedef struct {
   tag_type tag;
   FILE *fp;
   int mode;
+  unsigned char flags;
   char *mem_buf;
   size_t mem_buf_len;
 } port_type;
@@ -790,6 +791,18 @@ typedef struct {
   p.tag = port_tag; \
   p.fp = f; \
   p.mode = m; \
+  p.flags = 0; \
+  p.mem_buf = NULL; \
+  p.mem_buf_len = 0;
+
+#define make_file_backed_port(p,f,m) \
+  port_type p; \
+  p.hdr.mark = gc_color_red; \
+  p.hdr.grayed = 0; \
+  p.tag = port_tag; \
+  p.fp = f; \
+  p.mode = m; \
+  p.flags = 1; \
   p.mem_buf = NULL; \
   p.mem_buf_len = 0;