diff --git a/src/testium/main_win/test_file_manager.py b/src/testium/main_win/test_file_manager.py
index 4b58aaa..a05f567 100644
--- a/src/testium/main_win/test_file_manager.py
+++ b/src/testium/main_win/test_file_manager.py
@@ -212,8 +212,17 @@ class TestFileManager:
         d = ""
         if w.testFile is not None:
             d = os.path.dirname(w.testFile)
+        # In Flatpak the native dialog goes through the XDG document portal,
+        # which returns /run/user/UID/doc/.../test.tum and only exposes the
+        # selected file — sibling files (param.yaml, .py, etc.) are unreachable.
+        # Force Qt's own dialog, which walks the real filesystem mounted via
+        # --filesystem=home and returns a regular path with sibling access.
+        options = QFileDialog.Options()
+        if os.path.isfile("/.flatpak-info"):
+            options |= QFileDialog.Option.DontUseNativeDialog
         file_name, _ = QFileDialog.getOpenFileName(
-            w, "Open the test file", d, "testium file (*.tum);;All Files (*)"
+            w, "Open the test file", d,
+            "testium file (*.tum);;All Files (*)", options=options
         )
         if file_name:
             self.reload(file_name)