diff --git a/gtk/gtkbuilder.c b/gtk/gtkbuilder.c
index 7b7c166f46..b0775d2907 100644
--- a/gtk/gtkbuilder.c
+++ b/gtk/gtkbuilder.c
@@ -1784,7 +1784,7 @@ gtk_builder_value_from_string (GtkBuilder   *builder,
       gunichar c;
       g_value_init (value, G_TYPE_UINT);
       c = g_utf8_get_char_validated (string, strlen (string));
-      if (c > 0)
+      if (c != 0 && c != (gunichar)-1 && c != (gunichar)-2)
         g_value_set_uint (value, c);
       return TRUE;
     }
diff --git a/modules/input/gtkimcontextthai.c b/modules/input/gtkimcontextthai.c
index 254dfc78fc..73510c0360 100644
--- a/modules/input/gtkimcontextthai.c
+++ b/modules/input/gtkimcontextthai.c
@@ -195,7 +195,7 @@ get_previous_char (GtkIMContextThai *context_thai, gint offset)
       if (offset == 0)
         {
           prev_char = g_utf8_get_char_validated (q, p - q);
-          if (prev_char < 0)
+          if (prev_char == (gunichar)-1 || prev_char == (gunichar)-2)
             prev_char = 0;
         }
       g_free (surrounding);