diff --git a/src/poetry/installation/installer.py b/src/poetry/installation/installer.py
index 287a180a111..e3cdcb9e0ed 100644
--- a/src/poetry/installation/installer.py
+++ b/src/poetry/installation/installer.py
@@ -201,6 +201,8 @@ def _do_refresh(self) -> int:
             self._io,
         )
 
+        # Always re-solve directory dependencies, otherwise we can't determine
+        # if anything has changed (and the lock file contains an invalid version).
         use_latest = [
             p.name for p in locked_repository.packages if p.source_type == "directory"
         ]
diff --git a/tests/console/commands/test_lock.py b/tests/console/commands/test_lock.py
index 7f78a22ec67..a8ef7c2aac9 100644
--- a/tests/console/commands/test_lock.py
+++ b/tests/console/commands/test_lock.py
@@ -179,6 +179,12 @@ def test_lock_no_update_path_dependencies(
     poetry_with_nested_path_deps_old_lockfile: Poetry,
     repo: TestRepository,
 ):
+    """
+    The lock file contains a variant of the directory dependency "quix" that does
+    not depend on "sampleproject". Although the version of "quix" has not been changed,
+    it should be re-solved because there is always only one valid version
+    of a directory dependency at any time.
+    """
     repo.add_package(get_package("sampleproject", "1.3.1"))
 
     locker = Locker(