diff --git a/picard/acoustid/__init__.py b/picard/acoustid/__init__.py
index 20be0ed8bb..fce1b386ba 100644
--- a/picard/acoustid/__init__.py
+++ b/picard/acoustid/__init__.py
@@ -260,6 +260,8 @@ def _run_next_task(self):
         process.finished.connect(partial(self._on_fpcalc_finished, task))
         process.error.connect(partial(self._on_fpcalc_error, task))
         file_path = task.file.filename
+        # On Windows fpcalc.exe does not handle long paths, even if system wide
+        # long path support is enabled. Ensure the path is properly prefixed.
         if IS_WIN:
             file_path = win_prefix_longpath(file_path)
         process.start(self._fpcalc, ["-json", "-length", "120", file_path])