diff --git a/lib/python/pyflyby/_importdb.py b/lib/python/pyflyby/_importdb.py
index 4df4186e..818121f2 100644
--- a/lib/python/pyflyby/_importdb.py
+++ b/lib/python/pyflyby/_importdb.py
@@ -284,7 +284,7 @@ def get_default(cls, target_filename: Union[Filename, str], /):
         target_path = Path(target_filename).resolve()
 
         parents: List[Path]
-        if not target_path.is_dir():
+        if target_path.is_dir():
             parents = [target_path]
         else:
             parents = []
diff --git a/tests/test_importdb.py b/tests/test_importdb.py
index 80bdb8a4..438f6ac4 100644
--- a/tests/test_importdb.py
+++ b/tests/test_importdb.py
@@ -6,6 +6,7 @@
 
 
 import os
+import sys
 from   shutil                   import rmtree
 from   tempfile                 import NamedTemporaryFile, mkdtemp
 from   textwrap                 import dedent
@@ -15,8 +16,31 @@
 from   pyflyby._importstmt      import Import
 from   pyflyby._util            import EnvVarCtx
 
+from contextlib import contextmanager
 
 
+if sys.version_info > (3, 11):
+    from contextlib import chdir
+
+else:
+
+    @contextmanager
+    def chdir(path):
+        old = os.getcwd()
+        try:
+            os.chdir(path)
+            yield
+        finally:
+            os.chdir(old)
+
+
+def test_importDB_root():
+    """
+    See #362
+    """
+    with chdir("/"):
+        ImportDB.get_default(None)
+
 def test_ImportDB_from_code_1():
     db = ImportDB('from aa.bb import cc as dd, ee')
     expected_known = ImportSet(['from aa.bb import cc as dd, ee'])