diff --git a/generator/c.ml b/generator/c.ml
index 6236ed496..7357381b7 100644
--- a/generator/c.ml
+++ b/generator/c.ml
@@ -1067,9 +1067,9 @@ and generate_client_actions hash () =
       pr "\n"
     );
 
-    pr "    trace_fp = guestfs___trace_open (g);\n";
+    pr "    guestfs___trace_open (&trace_buffer);\n";
 
-    pr "    fprintf (trace_fp, \"%%s\", \"%s\");\n" name;
+    pr "    fprintf (trace_buffer.fp, \"%%s\", \"%s\");\n" name;
 
     (* Required arguments. *)
     List.iter (
@@ -1082,33 +1082,35 @@ and generate_client_actions hash () =
       | FileIn n
       | FileOut n ->
           (* guestfish doesn't support string escaping, so neither do we *)
-          pr "    fprintf (trace_fp, \" \\\"%%s\\\"\", %s);\n" n
+          pr "    fprintf (trace_buffer.fp, \" \\\"%%s\\\"\", %s);\n" n
       | Key n ->
           (* don't print keys *)
-          pr "    fprintf (trace_fp, \" \\\"***\\\"\");\n"
+          pr "    fprintf (trace_buffer.fp, \" \\\"***\\\"\");\n"
       | OptString n ->			(* string option *)
-          pr "    if (%s) fprintf (trace_fp, \" \\\"%%s\\\"\", %s);\n" n n;
-          pr "    else fprintf (trace_fp, \" null\");\n"
+          pr "    if (%s)\n" n;
+          pr "      fprintf (trace_buffer.fp, \" \\\"%%s\\\"\", %s);\n" n;
+          pr "    else\n";
+          pr "      fprintf (trace_buffer.fp, \" null\");\n"
       | StringList n
       | DeviceList n ->			(* string list *)
-          pr "    fputc (' ', trace_fp);\n";
-          pr "    fputc ('\"', trace_fp);\n";
+          pr "    fputc (' ', trace_buffer.fp);\n";
+          pr "    fputc ('\"', trace_buffer.fp);\n";
           pr "    for (i = 0; %s[i]; ++i) {\n" n;
-          pr "      if (i > 0) fputc (' ', trace_fp);\n";
-          pr "      fputs (%s[i], trace_fp);\n" n;
+          pr "      if (i > 0) fputc (' ', trace_buffer.fp);\n";
+          pr "      fputs (%s[i], trace_buffer.fp);\n" n;
           pr "    }\n";
-          pr "    fputc ('\"', trace_fp);\n";
+          pr "    fputc ('\"', trace_buffer.fp);\n";
       | Bool n ->			(* boolean *)
-          pr "    fputs (%s ? \" true\" : \" false\", trace_fp);\n" n
+          pr "    fputs (%s ? \" true\" : \" false\", trace_buffer.fp);\n" n
       | Int n ->			(* int *)
-          pr "    fprintf (trace_fp, \" %%d\", %s);\n" n
+          pr "    fprintf (trace_buffer.fp, \" %%d\", %s);\n" n
       | Int64 n ->
-          pr "    fprintf (trace_fp, \" %%\" PRIi64, %s);\n" n
+          pr "    fprintf (trace_buffer.fp, \" %%\" PRIi64, %s);\n" n
       | BufferIn n ->                   (* RHBZ#646822 *)
-          pr "    fputc (' ', trace_fp);\n";
-          pr "    guestfs___print_BufferIn (trace_fp, %s, %s_size);\n" n n
+          pr "    fputc (' ', trace_buffer.fp);\n";
+          pr "    guestfs___print_BufferIn (trace_buffer.fp, %s, %s_size);\n" n n
       | Pointer (t, n) ->
-          pr "    fprintf (trace_fp, \" (%s)%%p\", %s);\n" t n
+          pr "    fprintf (trace_buffer.fp, \" (%s)%%p\", %s);\n" t n
     ) args;
 
     (* Optional arguments. *)
@@ -1119,25 +1121,25 @@ and generate_client_actions hash () =
           (String.uppercase c_name) (String.uppercase n);
         (match argt with
          | OString n ->
-             pr "      fprintf (trace_fp, \" \\\"%%s:%%s\\\"\", \"%s\", optargs->%s);\n" n n
+             pr "      fprintf (trace_buffer.fp, \" \\\"%%s:%%s\\\"\", \"%s\", optargs->%s);\n" n n
          | OStringList n ->
-             pr "      fprintf (trace_fp, \" \\\"%%s:\", \"%s\");\n" n;
+             pr "      fprintf (trace_buffer.fp, \" \\\"%%s:\", \"%s\");\n" n;
              pr "      for (i = 0; optargs->%s[i] != NULL; ++i) {\n" n;
-             pr "        if (i > 0) fputc (' ', trace_fp);\n";
-             pr "        fputs (optargs->%s[i], trace_fp);\n" n;
+             pr "        if (i > 0) fputc (' ', trace_buffer.fp);\n";
+             pr "        fputs (optargs->%s[i], trace_buffer.fp);\n" n;
              pr "      }\n";
-             pr "      fputc ('\\\"', trace_fp);\n"
+             pr "      fputc ('\\\"', trace_buffer.fp);\n"
          | OBool n ->
-             pr "      fprintf (trace_fp, \" \\\"%%s:%%s\\\"\", \"%s\", optargs->%s ? \"true\" : \"false\");\n" n n
+             pr "      fprintf (trace_buffer.fp, \" \\\"%%s:%%s\\\"\", \"%s\", optargs->%s ? \"true\" : \"false\");\n" n n
          | OInt n ->
-             pr "      fprintf (trace_fp, \" \\\"%%s:%%d\\\"\", \"%s\", optargs->%s);\n" n n
+             pr "      fprintf (trace_buffer.fp, \" \\\"%%s:%%d\\\"\", \"%s\", optargs->%s);\n" n n
          | OInt64 n ->
-             pr "      fprintf (trace_fp, \" \\\"%%s:%%\" PRIi64 \"\\\"\", \"%s\", optargs->%s);\n" n n
+             pr "      fprintf (trace_buffer.fp, \" \\\"%%s:%%\" PRIi64 \"\\\"\", \"%s\", optargs->%s);\n" n n
         );
         pr "    }\n"
     ) optargs;
 
-    pr "    guestfs___trace_send_line (g);\n";
+    pr "    guestfs___trace_send_line (g, &trace_buffer);\n";
     pr "  }\n";
     pr "\n";
   in
@@ -1156,43 +1158,43 @@ and generate_client_actions hash () =
       pr "\n"
     );
 
-    pr "%s  trace_fp = guestfs___trace_open (g);\n" indent;
+    pr "%s  guestfs___trace_open (&trace_buffer);\n" indent;
 
-    pr "%s  fprintf (trace_fp, \"%%s = \", \"%s\");\n" indent name;
+    pr "%s  fprintf (trace_buffer.fp, \"%%s = \", \"%s\");\n" indent name;
 
     (match ret with
      | RErr | RInt _ | RBool _ ->
-         pr "%s  fprintf (trace_fp, \"%%d\", %s);\n" indent rv
+         pr "%s  fprintf (trace_buffer.fp, \"%%d\", %s);\n" indent rv
      | RInt64 _ ->
-         pr "%s  fprintf (trace_fp, \"%%\" PRIi64, %s);\n" indent rv
+         pr "%s  fprintf (trace_buffer.fp, \"%%\" PRIi64, %s);\n" indent rv
      | RConstString _ | RString _ ->
-         pr "%s  fprintf (trace_fp, \"\\\"%%s\\\"\", %s);\n" indent rv
+         pr "%s  fprintf (trace_buffer.fp, \"\\\"%%s\\\"\", %s);\n" indent rv
      | RConstOptString _ ->
-         pr "%s  fprintf (trace_fp, \"\\\"%%s\\\"\", %s != NULL ? %s : \"NULL\");\n"
+         pr "%s  fprintf (trace_buffer.fp, \"\\\"%%s\\\"\", %s != NULL ? %s : \"NULL\");\n"
            indent rv rv
      | RBufferOut _ ->
-         pr "%s  guestfs___print_BufferOut (trace_fp, %s, *size_r);\n" indent rv
+         pr "%s  guestfs___print_BufferOut (trace_buffer.fp, %s, *size_r);\n" indent rv
      | RStringList _ | RHashtable _ ->
-         pr "%s  fputs (\"[\", trace_fp);\n" indent;
+         pr "%s  fputs (\"[\", trace_buffer.fp);\n" indent;
          pr "%s  for (i = 0; %s[i]; ++i) {\n" indent rv;
-         pr "%s    if (i > 0) fputs (\", \", trace_fp);\n" indent;
-         pr "%s    fputs (\"\\\"\", trace_fp);\n" indent;
-         pr "%s    fputs (%s[i], trace_fp);\n" indent rv;
-         pr "%s    fputs (\"\\\"\", trace_fp);\n" indent;
+         pr "%s    if (i > 0) fputs (\", \", trace_buffer.fp);\n" indent;
+         pr "%s    fputs (\"\\\"\", trace_buffer.fp);\n" indent;
+         pr "%s    fputs (%s[i], trace_buffer.fp);\n" indent rv;
+         pr "%s    fputs (\"\\\"\", trace_buffer.fp);\n" indent;
          pr "%s  }\n" indent;
-         pr "%s  fputs (\"]\", trace_fp);\n" indent;
+         pr "%s  fputs (\"]\", trace_buffer.fp);\n" indent;
      | RStruct (_, typ) ->
          (* XXX There is code generated for guestfish for printing
           * these structures.  We need to make it generally available
           * for all callers
           *)
-         pr "%s  fprintf (trace_fp, \"<struct guestfs_%s *>\");\n"
+         pr "%s  fprintf (trace_buffer.fp, \"<struct guestfs_%s *>\");\n"
            indent typ (* XXX *)
      | RStructList (_, typ) ->
-         pr "%s  fprintf (trace_fp, \"<struct guestfs_%s_list *>\");\n"
+         pr "%s  fprintf (trace_buffer.fp, \"<struct guestfs_%s_list *>\");\n"
            indent typ (* XXX *)
     );
-    pr "%s  guestfs___trace_send_line (g);\n" indent;
+    pr "%s  guestfs___trace_send_line (g, &trace_buffer);\n" indent;
     pr "%s}\n" indent;
     pr "\n";
   in
@@ -1236,7 +1238,7 @@ and generate_client_actions hash () =
     handle_null_optargs optargs c_name;
 
     pr "  int trace_flag = g->trace;\n";
-    pr "  FILE *trace_fp;\n";
+    pr "  struct trace_buffer trace_buffer;\n";
     (match ret with
     | RErr | RInt _ | RBool _ ->
       pr "  int r;\n"
@@ -1339,7 +1341,7 @@ and generate_client_actions hash () =
     pr "  int serial;\n";
     pr "  int r;\n";
     pr "  int trace_flag = g->trace;\n";
-    pr "  FILE *trace_fp;\n";
+    pr "  struct trace_buffer trace_buffer;\n";
     (match ret with
     | RErr | RInt _ | RBool _ -> pr "  int ret_v;\n"
     | RInt64 _ -> pr "  int64_t ret_v;\n"
diff --git a/src/actions-support.c b/src/actions-support.c
index 461a349e1..865567863 100644
--- a/src/actions-support.c
+++ b/src/actions-support.c
@@ -77,37 +77,31 @@ guestfs___check_appliance_up (guestfs_h *g, const char *caller)
 }
 
 /* Convenience wrapper for tracing. */
-FILE *
-guestfs___trace_open (guestfs_h *g)
+void
+guestfs___trace_open (struct trace_buffer *tb)
 {
-  assert (g->trace_fp == NULL);
-  g->trace_buf = NULL;
-  g->trace_len = 0;
-  g->trace_fp = open_memstream (&g->trace_buf, &g->trace_len);
-  if (g->trace_fp)
-    return g->trace_fp;
-  else
-    return stderr;
+  tb->buf = NULL;
+  tb->len = 0;
+  tb->fp = open_memstream (&tb->buf, &tb->len);
+  if (tb->fp)
+    tb->opened = true;
+  else {
+    tb->opened = false;
+    /* Fall back to writing messages to stderr. */
+    free (tb->buf);
+    tb->buf = NULL;
+    tb->fp = stderr;
+  }
 }
 
 void
-guestfs___trace_send_line (guestfs_h *g)
+guestfs___trace_send_line (guestfs_h *g, struct trace_buffer *tb)
 {
-  char *buf;
-  size_t len;
-
-  if (g->trace_fp) {
-    fclose (g->trace_fp);
-    g->trace_fp = NULL;
-
-    /* The callback might invoke other libguestfs calls, so keep
-     * a copy of the pointer to the buffer and length.
-     */
-    buf = g->trace_buf;
-    len = g->trace_len;
-    g->trace_buf = NULL;
-    guestfs___call_callbacks_message (g, GUESTFS_EVENT_TRACE, buf, len);
-
-    free (buf);
+  if (tb->opened) {
+    fclose (tb->fp);
+    tb->fp = NULL;
+    guestfs___call_callbacks_message (g, GUESTFS_EVENT_TRACE, tb->buf, tb->len);
+    free (tb->buf);
+    tb->buf = NULL;
   }
 }
diff --git a/src/guestfs-internal.h b/src/guestfs-internal.h
index c25b89323..6743189ec 100644
--- a/src/guestfs-internal.h
+++ b/src/guestfs-internal.h
@@ -246,11 +246,6 @@ struct guestfs_h
   struct hash_table *pda;
   struct pda_entry *pda_next;
 
-  /* Used by src/actions.c:trace_* functions. */
-  FILE *trace_fp;
-  char *trace_buf;
-  size_t trace_len;
-
   /* User cancelled transfer.  Not signal-atomic, but it doesn't
    * matter for this case because we only care if it is != 0.
    */
@@ -461,10 +456,17 @@ extern void guestfs___print_BufferOut (FILE *out, const char *buf, size_t buf_si
   while (0)
 
 /* actions-support.c */
+struct trace_buffer {
+  FILE *fp;
+  char *buf;
+  size_t len;
+  bool opened;
+};
+
 extern int guestfs___check_reply_header (guestfs_h *g, const struct guestfs_message_header *hdr, unsigned int proc_nr, unsigned int serial);
 extern int guestfs___check_appliance_up (guestfs_h *g, const char *caller);
-extern FILE *guestfs___trace_open (guestfs_h *g);
-extern void guestfs___trace_send_line (guestfs_h *g);
+extern void guestfs___trace_open (struct trace_buffer *tb);
+extern void guestfs___trace_send_line (guestfs_h *g, struct trace_buffer *tb);
 
 /* match.c */
 extern int guestfs___match (guestfs_h *g, const char *str, const pcre *re);