diff --git a/src/gui/gtk.c b/src/gui/gtk.c
index 7ccadb27c898..00f4ab2e4136 100644
--- a/src/gui/gtk.c
+++ b/src/gui/gtk.c
@@ -3686,9 +3686,20 @@ void dt_gui_load_theme(const char *theme)
 
   GError *error = NULL;
 
-  GtkStyleProvider *themes_style_provider = GTK_STYLE_PROVIDER(gtk_css_provider_new());
-  gtk_style_context_add_provider_for_screen
-    (gdk_screen_get_default(), themes_style_provider, GTK_STYLE_PROVIDER_PRIORITY_USER + 1);
+  // Reuse a single provider across calls. Adding a fresh one each time
+  // leaked the previous theme onto the screen -- gtk keeps its own
+  // reference, so the unref below never removed it -- and with every
+  // provider sitting at the same priority the oldest one still won the
+  // @define-color lookups. The result was a theme change only taking
+  // effect one load later.
+  static GtkCssProvider *themes_style_provider = NULL;
+  if(!themes_style_provider)
+  {
+    themes_style_provider = gtk_css_provider_new();
+    gtk_style_context_add_provider_for_screen
+      (gdk_screen_get_default(), GTK_STYLE_PROVIDER(themes_style_provider),
+       GTK_STYLE_PROVIDER_PRIORITY_USER + 1);
+  }
 
   // We load the themes in this specific order:
   //   1. The main darktable-*.css
@@ -3739,7 +3750,7 @@ void dt_gui_load_theme(const char *theme)
     themecss = newcss;
   }
 
-  if(!gtk_css_provider_load_from_data(GTK_CSS_PROVIDER(themes_style_provider),
+  if(!gtk_css_provider_load_from_data(themes_style_provider,
                                       themecss, -1, &error))
   {
     dt_print(DT_DEBUG_ALWAYS,
@@ -3749,8 +3760,7 @@ void dt_gui_load_theme(const char *theme)
   }
 
   g_free(themecss);
-
-  g_object_unref(themes_style_provider);
+  // provider is kept alive on purpose, see above
 }
 
 void dt_gui_apply_theme()
diff --git a/src/gui/preferences.c b/src/gui/preferences.c
index ef3f89ab8ecd..112756fdae06 100644
--- a/src/gui/preferences.c
+++ b/src/gui/preferences.c
@@ -393,7 +393,9 @@ static void init_tab_general(GtkWidget *dialog,
 
   // read all themes
   char *theme_name = dt_conf_get_string("ui_last/theme");
-  int selected = 0;
+  const char *default_theme = dt_confgen_get("ui_last/theme", DT_DEFAULT);
+  int selected = -1;
+  int default_selected = -1;
   int k = 0;
   for(GList *iter = darktable.themes; iter; iter = g_list_next(iter))
   {
@@ -403,10 +405,17 @@ static void init_tab_general(GtkWidget *dialog,
     if(i) *i = '\0';
     dt_bauhaus_combobox_add_aligned(widget, name, DT_BAUHAUS_COMBOBOX_ALIGN_LEFT);
     if(!g_strcmp0(name, theme_name)) selected = k;
+    if(!g_strcmp0(name, default_theme)) default_selected = k;
     k++;
+    g_free(name);
   }
   g_free(theme_name);
 
+  // a theme we don't know about must not silently read as whichever one
+  // happens to sort first -- show the configured default instead
+  if(selected < 0)
+    selected = (default_selected >= 0) ? default_selected : 0;
+
   dt_bauhaus_combobox_set(widget, selected);
 
   g_signal_connect(G_OBJECT(widget), "value-changed",