diff --git a/src/source_dialog.cpp b/src/source_dialog.cpp
index 8bc7d32..7889003 100644
--- a/src/source_dialog.cpp
+++ b/src/source_dialog.cpp
@@ -470,7 +470,7 @@ void form_rebuild(Chooser& c, SourceKind& kind, const SourceConfig& initial) {
       c.form_cfg.description.empty() ? nullptr : c.form_cfg.description.c_str());
   c.form_cfg.write(initial);
   c.form_cfg.on_change([&c] {
-    if (c.form_connect != nullptr) {
+    if (c.form_connect != nullptr && c.form_cfg.valid) {
       gtk_widget_set_sensitive(c.form_connect, c.form_cfg.valid() ? TRUE : FALSE);
     }
   });
@@ -570,6 +570,18 @@ void open_form(Chooser& c, int edit_index = -1) {
       edit_index >= 0 && static_cast<std::size_t>(edit_index) < c.known.size()
           ? &c.known[static_cast<std::size_t>(edit_index)]
           : nullptr;
+  // An edit of a session whose kind is not registered is refused: the form would rebuild as the first
+  // kind, and Save would rewrite the file as that kind and delete the original.
+  if (src != nullptr && !src->kind.empty()) {
+    bool known_kind = false;
+    for (SourceKind* k : kinds()) known_kind = known_kind || k->id() == src->kind;
+    if (!known_kind) {
+      std::fprintf(stderr, "[sources] cannot edit %s: source kind '%s' is not registered\n",
+                   src->config.c_str(), src->kind.c_str());
+      std::fflush(stderr);
+      return;
+    }
+  }
   c.edit_host = src != nullptr ? src->host : std::string();
   c.edit_port = src != nullptr ? src->port : 0;
   c.edit_config = src != nullptr ? src->config : std::string();
@@ -668,6 +680,8 @@ void open_form(Chooser& c, int edit_index = -1) {
                      ch.form_cfg_rows.clear();
                      ch.form_kind_row = nullptr;
                      ch.form_source_group = nullptr;
+                     ch.form_connect = nullptr;
+                     ch.form_kinds.clear();
                    }),
                    &c);