diff --git a/generator/bindtests.ml b/generator/bindtests.ml
index 78b0c8ddb..9f459ac2f 100644
--- a/generator/bindtests.ml
+++ b/generator/bindtests.ml
@@ -131,7 +131,8 @@ print_strings (guestfs_h *g, char *const *argv)
         | String n
         | FileIn n
         | FileOut n
-        | Key n -> pr "  fprintf (fp, \"%%s\\n\", %s);\n" n
+        | Key n
+        | GUID n -> pr "  fprintf (fp, \"%%s\\n\", %s);\n" n
         | BufferIn n ->
           pr "  {\n";
           pr "    size_t i;\n";
diff --git a/generator/c.ml b/generator/c.ml
index 5fbae74ce..e2d5754f2 100644
--- a/generator/c.ml
+++ b/generator/c.ml
@@ -122,7 +122,8 @@ let rec generate_prototype ?(extern = true) ?(static = false)
     | Device n | Dev_or_Path n
     | String n
     | OptString n
-    | Key n ->
+    | Key n
+    | GUID n ->
         next ();
         pr "const char *%s" n
     | Mountable n | Mountable_or_Path n ->
@@ -1243,7 +1244,8 @@ and generate_client_actions hash () =
       | StringList n
       | DeviceList n
       | Key n
-      | Pointer (_, n) ->
+      | Pointer (_, n)
+      | GUID n ->
           pr "  if (%s == NULL) {\n" n;
           pr "    error (g, \"%%s: %%s: parameter cannot be NULL\",\n";
           pr "           \"%s\", \"%s\");\n" c_name n;
@@ -1356,7 +1358,8 @@ and generate_client_actions hash () =
       | Pathname n
       | Dev_or_Path n | Mountable_or_Path n
       | FileIn n
-      | FileOut n ->
+      | FileOut n
+      | GUID n ->
           (* guestfish doesn't support string escaping, so neither do we *)
           pr "    fprintf (trace_buffer.fp, \" \\\"%%s\\\"\", %s);\n" n
       | Key n ->
@@ -1678,7 +1681,7 @@ and generate_client_actions hash () =
         function
         | Pathname n | Device n | Mountable n | Dev_or_Path n 
         | Mountable_or_Path n | String n
-        | Key n ->
+        | Key n | GUID n ->
           pr "  args.%s = (char *) %s;\n" n n
         | OptString n ->
           pr "  args.%s = %s ? (char **) &%s : NULL;\n" n n n
diff --git a/generator/csharp.ml b/generator/csharp.ml
index 536f532a6..c2b01bad2 100644
--- a/generator/csharp.ml
+++ b/generator/csharp.ml
@@ -192,7 +192,8 @@ namespace Guestfs
           | OptString n
           | FileIn n | FileOut n
           | Key n
-          | BufferIn n ->
+          | BufferIn n
+          | GUID n ->
               pr ", [In] string %s" n
           | StringList n | DeviceList n ->
               pr ", [In] string[] %s" n
@@ -220,7 +221,8 @@ namespace Guestfs
           | OptString n
           | FileIn n | FileOut n
           | Key n
-          | BufferIn n ->
+          | BufferIn n
+          | GUID n ->
               next (); pr "string %s" n
           | StringList n | DeviceList n ->
               next (); pr "string[] %s" n
diff --git a/generator/daemon.ml b/generator/daemon.ml
index 8a759f7c8..548982b52 100644
--- a/generator/daemon.ml
+++ b/generator/daemon.ml
@@ -250,7 +250,7 @@ cleanup_free_mountable (mountable_t *mountable)
           function
           | Device n | Dev_or_Path n ->
             pr "  CLEANUP_FREE char *%s = NULL;\n" n
-          | Pathname n | String n | Key n | OptString n ->
+          | Pathname n | String n | Key n | OptString n | GUID n ->
             pr "  const char *%s;\n" n
           | Mountable n | Mountable_or_Path n ->
             pr "  CLEANUP_FREE_MOUNTABLE mountable_t %s\n" n;
@@ -346,7 +346,7 @@ cleanup_free_mountable (mountable_t *mountable)
           | Mountable_or_Path n ->
               pr "  REQUIRE_ROOT_OR_RESOLVE_MOUNTABLE (args.%s, %s, %s, goto done);\n"
                 n n (if is_filein then "cancel_receive ()" else "");
-          | String n | Key n -> pr_args n
+          | String n | Key n | GUID n -> pr_args n
           | OptString n -> pr "  %s = args.%s ? *args.%s : NULL;\n" n n n
           | StringList n ->
             pr "  /* Ugly, but safe and avoids copying the strings. */\n";
diff --git a/generator/erlang.ml b/generator/erlang.ml
index b52cf1f38..f0c9c6af6 100644
--- a/generator/erlang.ml
+++ b/generator/erlang.ml
@@ -297,7 +297,8 @@ extern int64_t get_int64 (ETERM *term);
           | String n
           | FileIn n
           | FileOut n
-          | Key n ->
+          | Key n
+          | GUID n ->
             pr "  CLEANUP_FREE char *%s = erl_iolist_to_string (ARG (%d));\n" n i
           | OptString n ->
             pr "  CLEANUP_FREE char *%s;\n" n;
diff --git a/generator/fish.ml b/generator/fish.ml
index 7bde1ff19..477fb29b7 100644
--- a/generator/fish.ml
+++ b/generator/fish.ml
@@ -326,7 +326,8 @@ Guestfish will prompt for these separately."
         function
         | Device n | Mountable n
         | String n
-        | OptString n -> pr "  const char *%s;\n" n
+        | OptString n
+        | GUID n -> pr "  const char *%s;\n" n
         | Pathname n
         | Dev_or_Path n | Mountable_or_Path n
         | FileIn n
@@ -420,7 +421,7 @@ Guestfish will prompt for these separately."
       List.iter (
         function
         | Device name | Mountable name
-        | String name ->
+        | String name | GUID name ->
             pr "  %s = argv[i++];\n" name
         | Pathname name
         | Dev_or_Path name | Mountable_or_Path name ->
@@ -633,7 +634,8 @@ Guestfish will prompt for these separately."
         function
         | Device _ | Mountable _ | String _
         | OptString _
-        | BufferIn _ -> ()
+        | BufferIn _
+        | GUID _ -> ()
         | Bool name
         | Int name | Int64 name ->
             pr " out_%s:\n" name
@@ -865,7 +867,8 @@ and generate_fish_actions_pod () =
       List.iter (
         function
         | Pathname n | Device n | Mountable n
-        | Dev_or_Path n | Mountable_or_Path n | String n ->
+        | Dev_or_Path n | Mountable_or_Path n | String n
+        | GUID n ->
             pr " %s" n
         | OptString n -> pr " %s" n
         | StringList n | DeviceList n -> pr " '%s ...'" n
diff --git a/generator/gobject.ml b/generator/gobject.ml
index 4159c1e84..3cbc9c070 100644
--- a/generator/gobject.ml
+++ b/generator/gobject.ml
@@ -81,7 +81,8 @@ let generate_gobject_proto name ?(single_line = true)
       | OptString n
       | Key n
       | FileIn n
-      | FileOut n ->
+      | FileOut n
+      | GUID n ->
         pr "const gchar *%s" n
       | StringList n
       | DeviceList n ->
@@ -1031,7 +1032,7 @@ guestfs_session_close(GuestfsSession *session, GError **err)
             pr " (type gint32):"
           | Int64 _ ->
             pr " (type gint64):"
-          | String _ | Key _ ->
+          | String _ | Key _ | GUID _ ->
             pr " (transfer none) (type utf8):"
           | OptString _ ->
             pr " (transfer none) (type utf8) (allow-none):"
@@ -1190,7 +1191,8 @@ guestfs_session_close(GuestfsSession *session, GError **err)
           | Bool n | Int n | Int64 n | String n | Device n | Mountable n
           | Pathname n | Dev_or_Path n | Mountable_or_Path n
           | OptString n | StringList n
-          | DeviceList n | Key n | FileIn n | FileOut n ->
+          | DeviceList n | Key n | FileIn n | FileOut n
+          | GUID n ->
             pr "%s" n
           | Pointer _ ->
             failwith "gobject bindings do not support Pointer arguments"
diff --git a/generator/golang.ml b/generator/golang.ml
index 82c1a0d96..e67ca1b72 100644
--- a/generator/golang.ml
+++ b/generator/golang.ml
@@ -311,7 +311,8 @@ func return_hashtable (argv **C.char) map[string]string {
           | Dev_or_Path n
           | Mountable_or_Path n
           | Key n
-          | FileIn n | FileOut n -> pr "%s string" n
+          | FileIn n | FileOut n
+          | GUID n -> pr "%s string" n
           | OptString n -> pr "%s *string" n
           | StringList n
           | DeviceList n -> pr "%s []string" n
@@ -366,7 +367,8 @@ func return_hashtable (argv **C.char) map[string]string {
         | Dev_or_Path n
         | Mountable_or_Path n
         | Key n
-        | FileIn n | FileOut n ->
+        | FileIn n | FileOut n
+        | GUID n ->
           pr "\n";
           pr "    c_%s := C.CString (%s)\n" n n;
           pr "    defer C.free (unsafe.Pointer (c_%s))\n" n
@@ -450,7 +452,8 @@ func return_hashtable (argv **C.char) map[string]string {
           | Mountable_or_Path n
           | OptString n
           | Key n
-          | FileIn n | FileOut n -> pr "c_%s" n
+          | FileIn n | FileOut n
+          | GUID n -> pr "c_%s" n
           | StringList n
           | DeviceList n -> pr "c_%s" n
           | BufferIn n -> pr "c_%s, C.size_t (len (%s))" n n
diff --git a/generator/haskell.ml b/generator/haskell.ml
index 0329311b9..ca2a1ce27 100644
--- a/generator/haskell.ml
+++ b/generator/haskell.ml
@@ -142,7 +142,7 @@ assocListOfHashtable (a:b:rest) = (a,b) : assocListOfHashtable rest
           | FileOut n
           | Pathname n | Device n | Mountable n
           | Dev_or_Path n | Mountable_or_Path n | String n
-          | Key n ->
+          | Key n | GUID n ->
               pr "withCString %s $ \\%s -> " n n
           | BufferIn n ->
               pr "withCStringLen %s $ \\(%s, %s_size) -> " n n n
@@ -162,7 +162,7 @@ assocListOfHashtable (a:b:rest) = (a,b) : assocListOfHashtable rest
             | Dev_or_Path n | Mountable_or_Path n
             | String n | OptString n
             | StringList n | DeviceList n
-            | Key n -> n
+            | Key n | GUID n -> n
             | BufferIn n -> sprintf "%s (fromIntegral %s_size)" n n
           ) args in
         pr "withForeignPtr h (\\p -> c_%s %s)\n" name
@@ -218,7 +218,7 @@ and generate_haskell_prototype ~handle ?(hs = false) (ret, args, optargs) =
         (match arg with
         | Pathname _ | Device _ | Mountable _
         | Dev_or_Path _ | Mountable_or_Path _ | String _
-        | Key _ ->
+        | Key _ | GUID _ ->
           pr "CString"
         | BufferIn _ ->
           pr "CString -> CInt"
@@ -261,7 +261,7 @@ and generate_haskell_prototype ~handle ?(hs = false) (ret, args, optargs) =
         (match arg with
         | Pathname _ | Device _ | Mountable _
         | Dev_or_Path _ | Mountable_or_Path _ | String _
-        | Key _ ->
+        | Key _ | GUID _ ->
           pr "String"
         | BufferIn _ ->
           pr "String"
diff --git a/generator/java.ml b/generator/java.ml
index ec89f3ba3..2e5448392 100644
--- a/generator/java.ml
+++ b/generator/java.ml
@@ -452,7 +452,8 @@ and generate_java_prototype ?(public=false) ?(privat=false) ?(native=false)
       | OptString n
       | FileIn n
       | FileOut n
-      | Key n ->
+      | Key n
+      | GUID n ->
           pr "String %s" n
       | BufferIn n ->
           pr "byte[] %s" n
@@ -812,7 +813,8 @@ get_all_event_callbacks (guestfs_h *g, size_t *len_rtn)
         | OptString n
         | FileIn n
         | FileOut n
-        | Key n ->
+        | Key n
+        | GUID n ->
             pr ", jstring j%s" n
         | BufferIn n ->
             pr ", jbyteArray j%s" n
@@ -881,7 +883,8 @@ get_all_event_callbacks (guestfs_h *g, size_t *len_rtn)
         | OptString n
         | FileIn n
         | FileOut n
-        | Key n ->
+        | Key n
+        | GUID n ->
             pr "  const char *%s;\n" n
         | BufferIn n ->
             pr "  char *%s;\n" n;
@@ -937,7 +940,8 @@ get_all_event_callbacks (guestfs_h *g, size_t *len_rtn)
         | String n
         | FileIn n
         | FileOut n
-        | Key n ->
+        | Key n
+        | GUID n ->
             pr "  %s = (*env)->GetStringUTFChars (env, j%s, NULL);\n" n n
         | OptString n ->
             (* This is completely undocumented, but Java null becomes
@@ -1004,7 +1008,8 @@ get_all_event_callbacks (guestfs_h *g, size_t *len_rtn)
         | String n
         | FileIn n
         | FileOut n
-        | Key n ->
+        | Key n
+        | GUID n ->
             pr "  (*env)->ReleaseStringUTFChars (env, j%s, %s);\n" n n
         | OptString n ->
             pr "  if (j%s)\n" n;
diff --git a/generator/lua.ml b/generator/lua.ml
index 3d7c23831..9bd4006d3 100644
--- a/generator/lua.ml
+++ b/generator/lua.ml
@@ -461,7 +461,7 @@ guestfs_lua_delete_event_callback (lua_State *L)
         function
         | Pathname n | Device n | Mountable n
         | Dev_or_Path n | Mountable_or_Path n | String n
-        | FileIn n | FileOut n | Key n ->
+        | FileIn n | FileOut n | Key n | GUID n ->
           pr "  const char *%s;\n" n
         | BufferIn n ->
           pr "  const char *%s;\n" n;
@@ -492,7 +492,7 @@ guestfs_lua_delete_event_callback (lua_State *L)
           function
           | Pathname n | Device n | Mountable n
           | Dev_or_Path n | Mountable_or_Path n | String n
-          | FileIn n | FileOut n | Key n ->
+          | FileIn n | FileOut n | Key n | GUID n ->
             pr "  %s = luaL_checkstring (L, %d);\n" n i
           | BufferIn n ->
             pr "  %s = luaL_checklstring (L, %d, &%s_size);\n" n i n
@@ -556,7 +556,7 @@ guestfs_lua_delete_event_callback (lua_State *L)
         | FileIn _ | FileOut _ | Key _
         | BufferIn _ | OptString _
         | Bool _ | Int _ | Int64 _
-        | Pointer _ -> ()
+        | Pointer _ | GUID _ -> ()
         | StringList n | DeviceList n ->
           pr "  free (%s);\n" n
       ) args;
diff --git a/generator/ocaml.ml b/generator/ocaml.ml
index 2e8fc6414..78cff89e0 100644
--- a/generator/ocaml.ml
+++ b/generator/ocaml.ml
@@ -501,7 +501,8 @@ copy_table (char * const * argv)
         | String n
         | FileIn n
         | FileOut n
-        | Key n ->
+        | Key n
+        | GUID n ->
             (* Copy strings in case the GC moves them: RHBZ#604691 *)
             pr "  char *%s = guestfs___safe_strdup (g, String_val (%sv));\n" n n
         | OptString n ->
@@ -585,7 +586,8 @@ copy_table (char * const * argv)
         function
         | Pathname n | Device n | Mountable n
         | Dev_or_Path n | Mountable_or_Path n | String n
-        | OptString n | FileIn n | FileOut n | BufferIn n | Key n ->
+        | OptString n | FileIn n | FileOut n | BufferIn n
+        | Key n | GUID n ->
             pr "  free (%s);\n" n
         | StringList n | DeviceList n ->
             pr "  guestfs___free_string_list (%s);\n" n;
@@ -715,7 +717,8 @@ and generate_ocaml_function_type ?(extra_unit = false) (ret, args, optargs) =
     function
     | Pathname _ | Device _ | Mountable _
     | Dev_or_Path _ | Mountable_or_Path _ | String _
-    | FileIn _ | FileOut _ | BufferIn _ | Key _ -> pr "string -> "
+    | FileIn _ | FileOut _ | BufferIn _ | Key _
+    | GUID _ -> pr "string -> "
     | OptString _ -> pr "string option -> "
     | StringList _ | DeviceList _ -> pr "string array -> "
     | Bool _ -> pr "bool -> "
diff --git a/generator/perl.ml b/generator/perl.ml
index a87ea26c9..9d368a2cb 100644
--- a/generator/perl.ml
+++ b/generator/perl.ml
@@ -354,7 +354,7 @@ PREINIT:
           function
           | Pathname n | Device n | Mountable n
           | Dev_or_Path n | Mountable_or_Path n | String n
-          | FileIn n | FileOut n | Key n ->
+          | FileIn n | FileOut n | Key n | GUID n ->
               pr "      char *%s;\n" n
           | BufferIn n ->
               pr "      char *%s;\n" n;
@@ -509,7 +509,7 @@ PREINIT:
         | Dev_or_Path _ | Mountable_or_Path _ | String _
         | OptString _ | Bool _ | Int _ | Int64 _
         | FileIn _ | FileOut _
-        | BufferIn _ | Key _ | Pointer _ -> ()
+        | BufferIn _ | Key _ | Pointer _ | GUID _ -> ()
         | StringList n | DeviceList n -> pr "      free (%s);\n" n
       ) args;
 
@@ -937,7 +937,7 @@ errnos:
         | Dev_or_Path n -> pr "[ '%s', 'string(dev_or_path)', %d ]" n i
         | Mountable_or_Path n ->
           pr "[ '%s', 'string(mountable_or_path)', %d ]" n i
-        | String n -> pr "[ '%s', 'string', %d ]" n i
+        | String n | GUID n -> pr "[ '%s', 'string', %d ]" n i
         | FileIn n -> pr "[ '%s', 'string(filename)', %d ]" n i
         | FileOut n -> pr "[ '%s', 'string(filename)', %d ]" n i
         | Key n -> pr "[ '%s', 'string(key)', %d ]" n i
@@ -1105,7 +1105,7 @@ and generate_perl_prototype name (ret, args, optargs) =
       | Pathname n | Device n | Mountable n
       | Dev_or_Path n | Mountable_or_Path n | String n
       | OptString n | Bool n | Int n | Int64 n | FileIn n | FileOut n
-      | BufferIn n | Key n | Pointer (_, n) ->
+      | BufferIn n | Key n | Pointer (_, n) | GUID n ->
           pr "$%s" n
       | StringList n | DeviceList n ->
           pr "\\@%s" n
diff --git a/generator/php.ml b/generator/php.ml
index b7526f682..580b10fcc 100644
--- a/generator/php.ml
+++ b/generator/php.ml
@@ -192,7 +192,8 @@ PHP_FUNCTION (guestfs_last_error)
         | Dev_or_Path n | Mountable_or_Path n
         | FileIn n | FileOut n | Key n
         | OptString n
-        | BufferIn n ->
+        | BufferIn n
+        | GUID n ->
             pr "  char *%s;\n" n;
             pr "  int %s_size;\n" n
         | StringList n
@@ -235,7 +236,8 @@ PHP_FUNCTION (guestfs_last_error)
           function
           | String n | Device n | Mountable n | Pathname n
           | Dev_or_Path n | Mountable_or_Path n
-          | FileIn n | FileOut n | BufferIn n | Key n -> "s"
+          | FileIn n | FileOut n | BufferIn n | Key n
+          | GUID n -> "s"
           | OptString n -> "s!"
           | StringList n | DeviceList n -> "a"
           | Bool n -> "b"
@@ -269,7 +271,7 @@ PHP_FUNCTION (guestfs_last_error)
         | String n | Device n | Mountable n | Pathname n
         | Dev_or_Path n | Mountable_or_Path n
         | FileIn n | FileOut n | BufferIn n | Key n
-        | OptString n ->
+        | OptString n | GUID n ->
             pr ", &%s, &%s_size" n n
         | StringList n | DeviceList n ->
             pr ", &z_%s" n
@@ -303,7 +305,7 @@ PHP_FUNCTION (guestfs_last_error)
         | String n | Device n | Mountable n | Pathname n
         | Dev_or_Path n | Mountable_or_Path n
         | FileIn n | FileOut n | Key n
-        | OptString n ->
+        | OptString n | GUID n ->
             (* Just need to check the string doesn't contain any ASCII
              * NUL characters, which won't be supported by the C API.
              *)
@@ -434,7 +436,7 @@ PHP_FUNCTION (guestfs_last_error)
         | String n | Device n | Mountable n | Pathname n
         | Dev_or_Path n | Mountable_or_Path n
         | FileIn n | FileOut n | Key n
-        | OptString n -> ()
+        | OptString n | GUID n -> ()
         | BufferIn n -> ()
         | StringList n
         | DeviceList n ->
diff --git a/generator/python.ml b/generator/python.ml
index c6bfaaa44..607ca8824 100644
--- a/generator/python.ml
+++ b/generator/python.ml
@@ -281,7 +281,7 @@ put_table (char * const * const argv)
         function
         | Pathname n | Device n | Mountable n
         | Dev_or_Path n | Mountable_or_Path n | String n | Key n
-        | FileIn n | FileOut n ->
+        | FileIn n | FileOut n | GUID n ->
             pr "  const char *%s;\n" n
         | OptString n -> pr "  const char *%s;\n" n
         | BufferIn n ->
@@ -319,7 +319,7 @@ put_table (char * const * const argv)
         function
         | Pathname _ | Device _ | Mountable _
         | Dev_or_Path _ | Mountable_or_Path _ | String _ | Key _
-        | FileIn _ | FileOut _ -> pr "s"
+        | FileIn _ | FileOut _ | GUID _ -> pr "s"
         | OptString _ -> pr "z"
         | StringList _ | DeviceList _ -> pr "O"
         | Bool _ -> pr "i" (* XXX Python has booleans? *)
@@ -341,7 +341,7 @@ put_table (char * const * const argv)
         function
         | Pathname n | Device n | Mountable n
         | Dev_or_Path n | Mountable_or_Path n | String n | Key n
-        | FileIn n | FileOut n -> pr ", &%s" n
+        | FileIn n | FileOut n | GUID n -> pr ", &%s" n
         | OptString n -> pr ", &%s" n
         | StringList n | DeviceList n -> pr ", &py_%s" n
         | Bool n -> pr ", &%s" n
@@ -365,7 +365,7 @@ put_table (char * const * const argv)
         | Pathname _ | Device _ | Mountable _
         | Dev_or_Path _ | Mountable_or_Path _ | String _ | Key _
         | FileIn _ | FileOut _ | OptString _ | Bool _ | Int _ | Int64 _
-        | BufferIn _ -> ()
+        | BufferIn _ | GUID _ -> ()
         | StringList n | DeviceList n ->
             pr "  %s = get_string_list (py_%s);\n" n n;
             pr "  if (!%s) goto out;\n" n
@@ -502,7 +502,7 @@ put_table (char * const * const argv)
         | Pathname _ | Device _ | Mountable _
         | Dev_or_Path _ | Mountable_or_Path _ | String _ | Key _
         | FileIn _ | FileOut _ | OptString _ | Bool _ | Int _ | Int64 _
-        | BufferIn _ | Pointer _ -> ()
+        | BufferIn _ | Pointer _ | GUID _ -> ()
         | StringList n | DeviceList n ->
             pr "  free (%s);\n" n
       ) args;
@@ -796,7 +796,7 @@ class GuestFS(object):
         | Pathname _ | Device _ | Mountable _
         | Dev_or_Path _ | Mountable_or_Path _ | String _ | Key _
         | FileIn _ | FileOut _ | OptString _ | Bool _ | Int _ | Int64 _
-        | BufferIn _ | Pointer _ -> ()
+        | BufferIn _ | Pointer _ | GUID _ -> ()
         | StringList n | DeviceList n ->
             pr "        %s = list (%s)\n" n n
       ) args;
diff --git a/generator/ruby.ml b/generator/ruby.ml
index 6ba09dd4c..f2d700ee9 100644
--- a/generator/ruby.ml
+++ b/generator/ruby.ml
@@ -571,7 +571,7 @@ get_all_event_callbacks (guestfs_h *g, size_t *len_rtn)
         function
         | Pathname n | Device n | Mountable n
         | Dev_or_Path n | Mountable_or_Path n | String n | Key n
-        | FileIn n | FileOut n ->
+        | FileIn n | FileOut n | GUID n ->
           pr "  const char *%s = StringValueCStr (%sv);\n" n n;
         | BufferIn n ->
           pr "  Check_Type (%sv, T_STRING);\n" n;
@@ -675,7 +675,7 @@ get_all_event_callbacks (guestfs_h *g, size_t *len_rtn)
         | Pathname _ | Device _ | Mountable _
         | Dev_or_Path _ | Mountable_or_Path _ | String _ | Key _
         | FileIn _ | FileOut _ | OptString _ | Bool _ | Int _ | Int64 _
-        | BufferIn _ | Pointer _ -> ()
+        | BufferIn _ | Pointer _ | GUID _ -> ()
         | StringList n | DeviceList n ->
             pr "  free (%s);\n" n
       ) args;
diff --git a/generator/tests_c_api.ml b/generator/tests_c_api.ml
index 08ac13f78..c0ebcb9b2 100644
--- a/generator/tests_c_api.ml
+++ b/generator/tests_c_api.ml
@@ -384,7 +384,8 @@ and generate_test_command_call ?(expect_error = false) ?test ?ret test_name cmd=
     | Mountable_or_Path _, arg, sym
     | String _, arg, sym
     | OptString _, arg, sym
-    | Key _, arg, sym ->
+    | Key _, arg, sym
+    | GUID _, arg, sym ->
       pr "  const char *%s = \"%s\";\n" sym (c_quote arg);
     | BufferIn _, arg, sym ->
       pr "  const char *%s = \"%s\";\n" sym (c_quote arg);
@@ -504,7 +505,8 @@ and generate_test_command_call ?(expect_error = false) ?test ?ret test_name cmd=
     | String _, _, sym
     | OptString _, _, sym
     | Key _, _, sym
-    | FileIn _, _, sym -> pr ", %s" sym
+    | FileIn _, _, sym
+    | GUID _, _, sym -> pr ", %s" sym
     | BufferIn _, _, sym -> pr ", %s, %s_size" sym sym
     | FileOut _, arg, _ -> pr ", \"%s\"" (c_quote arg)
     | StringList _, _, sym | DeviceList _, _, sym -> pr ", (char **) %s" sym
diff --git a/generator/types.ml b/generator/types.ml
index 2827ea0d0..48ac32a51 100644
--- a/generator/types.ml
+++ b/generator/types.ml
@@ -184,6 +184,12 @@ and argt =
      * tests, although we should fix this in future.
      *)
   | Pointer of (string * string)
+    (* const char * which represents a GUID string.
+     *
+     * It cannot be NULL, and it will be validated using
+     * guestfs___validate_guid.
+     *)
+  | GUID of string
 
 and optargs = optargt list
 
diff --git a/generator/utils.ml b/generator/utils.ml
index 5828bbdd7..ecb35fd63 100644
--- a/generator/utils.ml
+++ b/generator/utils.ml
@@ -253,7 +253,8 @@ let name_of_argt = function
   | Pathname n | Device n | Mountable n | Dev_or_Path n
   | Mountable_or_Path n | String n | OptString n
   | StringList n | DeviceList n | Bool n | Int n | Int64 n
-  | FileIn n | FileOut n | BufferIn n | Key n | Pointer (_, n) -> n
+  | FileIn n | FileOut n | BufferIn n | Key n | Pointer (_, n)
+  | GUID n -> n
 
 let name_of_optargt = function
   | OBool n | OInt n | OInt64 n | OString n | OStringList n -> n
diff --git a/generator/xdr.ml b/generator/xdr.ml
index aa1fd5d56..257702a38 100644
--- a/generator/xdr.ml
+++ b/generator/xdr.ml
@@ -112,7 +112,7 @@ let generate_xdr () =
           function
           | Pathname n | Device n | Mountable n | Dev_or_Path n
           | Mountable_or_Path n | String n
-          | Key n ->
+          | Key n | GUID n ->
             pr "  string %s<>;\n" n
           | OptString n -> pr "  guestfs_str *%s;\n" n
           | StringList n | DeviceList n -> pr "  guestfs_str %s<>;\n" n