diff --git a/src/matrix-api.c b/src/matrix-api.c
index cf8fbb3..21a5411 100644
--- a/src/matrix-api.c
+++ b/src/matrix-api.c
@@ -911,7 +911,9 @@ matrix_api_list_public_rooms(MatrixAPI *api,
  * @error: return location for a #GError, or %NULL
  *
  * Ban the specified user from the specified room. An optional reason
- * can be specified.
+ * can be specified. If @room_id or @user_id is %NULL, this
+ * function returns immediately, and fills @error with
+ * %MATRIX_API_ERROR_INCOMPLETE.
  */
 void
 matrix_api_ban_user(MatrixAPI *api,
@@ -924,6 +926,14 @@ matrix_api_ban_user(MatrixAPI *api,
 {
     g_return_if_fail(MATRIX_IS_API(api));
 
+    if (!room_id || !user_id) {
+        g_set_error(error,
+                    MATRIX_API_ERROR, MATRIX_API_ERROR_INCOMPLETE,
+                    "room_id and user_id must be set.");
+
+        return;
+    }
+
     MATRIX_API_GET_IFACE(api)
         ->ban_user(api, callback, user_data, room_id, user_id, reason, error);
 }
@@ -947,6 +957,9 @@ matrix_api_ban_user(MatrixAPI *api,
  *
  * If the user is currently joined to the room, they will implicitly
  * leave the room as part of this API call.
+ *
+ * If @room_id is %NULL, this function returns immediately, and fills
+ * @error with %MATRIX_API_ERROR_INCOMPLETE.
  */
 void
 matrix_api_forget_room(MatrixAPI *api,
@@ -957,6 +970,14 @@ matrix_api_forget_room(MatrixAPI *api,
 {
     g_return_if_fail(MATRIX_IS_API(api));
 
+    if (!room_id) {
+        g_set_error(error,
+                    MATRIX_API_ERROR, MATRIX_API_ERROR_INCOMPLETE,
+                    "room_id must be set.");
+
+        return;
+    }
+
     MATRIX_API_GET_IFACE(api)
         ->forget_room(api, callback, user_data, room_id, error);
 }
@@ -969,11 +990,8 @@ matrix_api_forget_room(MatrixAPI *api,
  * @user_data: (closure): user data to pass to the callback function
  *             @callback
  * @room_id: the room ID to which to invite the user
- * @address: the invitee's 3rd party identifier
- * @medium: the kind of address being passed in the address field,
- *          e.g. <code>email</code>
- * @id_server: the hostname+port of the identity server which should
- *             be used for 3rd party identifier lookups
+ * @credential: (transfer none): a #MatrixAPI3PidCredential that
+ *              identifies a user to invite
  * @error: return location for a #GError, or %NULL
  *
  * Invite a user to the room by a 3rd party identifier. They do not
@@ -988,9 +1006,7 @@ void matrix_api_invite_user_3rdparty(MatrixAPI *api,
                                      MatrixAPICallback callback,
                                      gpointer user_data,
                                      const gchar *room_id,
-                                     const gchar *address,
-                                     const gchar *medium,
-                                     const gchar *id_server,
+                                     MatrixAPI3PidCredential *credential,
                                      GError **error)
 {
     g_return_if_fail(MATRIX_IS_API(api));
@@ -998,7 +1014,7 @@ void matrix_api_invite_user_3rdparty(MatrixAPI *api,
     MATRIX_API_GET_IFACE(api)
         ->invite_user_3rdparty(api,
                                callback, user_data,
-                               room_id, address, medium, id_server,
+                               room_id, credential,
                                error);
 }
 
diff --git a/src/matrix-api.h b/src/matrix-api.h
index 0e865c0..bda305e 100644
--- a/src/matrix-api.h
+++ b/src/matrix-api.h
@@ -212,9 +212,7 @@ struct _MatrixAPIInterface {
                                  MatrixAPICallback callback,
                                  gpointer user_data,
                                  const gchar *room_id,
-                                 const gchar *address,
-                                 const gchar *medium,
-                                 const gchar *id_server,
+                                 MatrixAPI3PidCredential *credential,
                                  GError **error);
     void (*invite_user)(MatrixAPI *api,
                         MatrixAPICallback callback,
@@ -635,9 +633,7 @@ void matrix_api_invite_user_3rdparty(MatrixAPI *api,
                                      MatrixAPICallback callback,
                                      gpointer user_data,
                                      const gchar *room_id,
-                                     const gchar *address,
-                                     const gchar *medium,
-                                     const gchar *id_server,
+                                     MatrixAPI3PidCredential *credential,
                                      GError **error);
 void matrix_api_invite_user(MatrixAPI *api,
                             MatrixAPICallback callback,
diff --git a/src/matrix-http-api.c b/src/matrix-http-api.c
index acf09a9..73650f5 100644
--- a/src/matrix-http-api.c
+++ b/src/matrix-http-api.c
@@ -1731,9 +1731,7 @@ i_invite_user_3rdparty(MatrixAPI *api,
                        MatrixAPICallback callback,
                        gpointer user_data,
                        const gchar *room_id,
-                       const gchar *address,
-                       const gchar *medium,
-                       const gchar *id_server,
+                       MatrixAPI3PidCredential *credential,
                        GError **error)
 {
     gchar *encoded_room_id, *path;
@@ -1744,21 +1742,10 @@ i_invite_user_3rdparty(MatrixAPI *api,
     path = g_strdup_printf("rooms/%s/invite", encoded_room_id);
     g_free(encoded_room_id);
 
-    builder = json_builder_new();
-    json_builder_begin_object(builder);
-
-    json_builder_set_member_name(builder, "id_server");
-    json_builder_add_string_value(builder, id_server);
-
-    json_builder_set_member_name(builder, "medium");
-    json_builder_add_string_value(builder, medium);
-
-    json_builder_set_member_name(builder, "address");
-    json_builder_add_string_value(builder, address);
-
-    json_builder_end_object(builder);
-    body = json_builder_get_root(builder);
-    g_object_unref(builder);
+    if ((body = matrix_api_3pid_credential_get_json_node(credential,
+                                                         error)) == NULL) {
+        return;
+    }
 
     _send(MATRIX_HTTP_API(api),
           callback, user_data,