diff --git a/src/puzzle-downloader.c b/src/puzzle-downloader.c
index 772f94428a33ab8da2e9e06d93428240a920f309..e819435a0b68e89a85d05f3977f87fe9528c57db 100644
--- a/src/puzzle-downloader.c
+++ b/src/puzzle-downloader.c
@@ -641,6 +641,45 @@ run_command (PuzzleDownloader     *downloader,
  * Input Dialogs
  */
 
+static DownloaderFormat
+file_format_from_file (GFile *file)
+{
+  g_autofree gchar *contents = NULL;
+  g_autoptr (GError) error = NULL;
+
+  if (!g_file_load_contents (file, NULL, &contents, NULL, NULL, &error))
+    {
+      g_warning ("Could not read file: %s\n", error->message);
+      return DOWNLOADER_FORMAT_UNKNOWN;
+    }
+
+  /* IPUZ files specify their IPUZ version with a URL to the spec.           */
+  if (strstr (contents, "http://ipuz.org/v2") != NULL)
+    return DOWNLOADER_FORMAT_IPUZ;
+  /* PUZ files contain a null-terminated magic string, "ACROSS&DOWN".        */
+  /* Because it's null-terminated, we can use g_strcmp0.                     */
+  else if ((strlen (contents) == 13)
+           && (g_strcmp0 (contents + 2, "ACROSS&DOWN") == 0))
+    return DOWNLOADER_FORMAT_PUZ;
+  /* JPZ files begin with an XML header.                                     */
+  else if (g_ascii_strncasecmp (contents, "<?xml", 5) == 0)
+    return DOWNLOADER_FORMAT_JPZ;
+  /* XD files can use an implicit order, with "\n\n\n" to separate sections. */
+  /* Or, they can use an explicit order, declaring sections with "##".       */
+  else if ((strstr (contents, "\n\n\n") != NULL)
+           || (strcasestr (contents, "## Grid")) != NULL)
+    return DOWNLOADER_FORMAT_XD;
+  return DOWNLOADER_FORMAT_UNKNOWN;
+}
+
+static DownloaderFormat
+file_format_from_uri (const gchar *uri)
+{
+  g_autoptr (GFile) file = NULL;
+  file = g_file_new_for_uri (uri);
+  return file_format_from_file (file);
+}
+
 static void
 file_dialog_copy_ready_cb (GFile            *source,
                            GAsyncResult     *res,
@@ -650,6 +689,8 @@ file_dialog_copy_ready_cb (GFile            *source,
   downloader_cancel_timeout_remove (downloader);
   g_clear_pointer (&downloader->cancel_dialog, adw_dialog_close);
 
+  downloader->format = file_format_from_file (source);
+
   if (downloader->format == DOWNLOADER_FORMAT_IPUZ)
     {
       g_autofree gchar *uri = NULL;
@@ -678,15 +719,12 @@ start_file_import (PuzzleDownloader *downloader)
 
   /* We can short circuit the download/conversion step if the file is
    * local and it's a .ipuz file. */
-  /* FIXME(mime): It would be nice to do mime-sniffing here for puz
-   * files, at least */
   /* FIXME(gio): g_file_query_filesystem_info might be a better
    * way to find out if it's local */
   if (strcmp (g_uri_peek_scheme (downloader->import_target_uri), "file") == 0)
     {
-      g_autofree char *filename = NULL;
-      filename = g_filename_from_uri (downloader->import_target_uri, NULL, NULL);
-      if (filename != NULL && g_str_has_suffix (filename, ".ipuz"))
+      downloader->format = file_format_from_uri (downloader->import_target_uri);
+      if (downloader->format == DOWNLOADER_FORMAT_IPUZ)
         {
           g_signal_emit (downloader, obj_signals [FINISHED], 0, downloader->import_target_uri, FALSE);
           g_clear_pointer (&downloader->import_target_uri, g_free);
@@ -704,22 +742,9 @@ start_file_import (PuzzleDownloader *downloader)
       g_warning ("Unable to create a tmp file: %s", error->message);
       return;
     }
-  /* FIXME(mime): we really need to add sniffing */
-  basename = g_file_get_basename (source);
-  if (g_str_has_suffix (basename, ".puz"))
-    downloader->format = DOWNLOADER_FORMAT_PUZ;
-  else if (g_str_has_suffix (basename, ".jpz") ||
-           g_str_has_suffix (basename, ".xml"))
-    downloader->format = DOWNLOADER_FORMAT_JPZ;
-  else if (g_str_has_suffix (basename, ".xd"))
-    downloader->format = DOWNLOADER_FORMAT_XD;
-  else
-    downloader->format = DOWNLOADER_FORMAT_IPUZ;
-
-  if (downloader->format != DOWNLOADER_FORMAT_IPUZ)
-    downloader->temp_file = g_file_get_path (destination);
 
   downloader_cancel_timeout_add (downloader, 2000, (GSourceFunc) downloader_cancel_timeout_cb);
+  downloader->temp_file = g_file_get_path (destination);
   downloader->wait_cancellable = g_cancellable_new ();
 
   flags = G_FILE_COPY_OVERWRITE;
@@ -776,6 +801,7 @@ run_file_dialog (PuzzleDownloader *downloader)
   gtk_file_filter_add_pattern (filter, "*.puz");
   gtk_file_filter_add_pattern (filter, "*.xml");
   gtk_file_filter_add_pattern (filter, "*.jpz");
+  gtk_file_filter_add_pattern (filter, "*.jpuz");
   gtk_file_filter_add_pattern (filter, "*.xd");
   g_list_store_append (filters, filter);
   gtk_file_dialog_set_default_filter (file_dialog, filter);
@@ -806,6 +832,12 @@ run_file_dialog (PuzzleDownloader *downloader)
   g_list_store_append (filters, filter);
   g_object_unref (filter);
 
+  filter = gtk_file_filter_new();
+  gtk_file_filter_set_name(filter, "All Files");
+  gtk_file_filter_add_pattern(filter, "*");
+  g_list_store_append (filters, filter);
+  g_object_unref (filter);
+
   gtk_file_dialog_set_filters (file_dialog, G_LIST_MODEL (filters));
 
   gtk_file_dialog_open (file_dialog, downloader->parent_window, NULL,