diff --git a/datasette/cli.py b/datasette/cli.py
index 9d1b5ee5..61e7ce91 100644
--- a/datasette/cli.py
+++ b/datasette/cli.py
@@ -549,6 +549,9 @@ def serve(
                     )
                 )
 
+    # De-duplicate files so 'datasette db.db db.db' only attaches one /db
+    files = list(dict.fromkeys(files))
+
     try:
         ds = Datasette(files, **kwargs)
     except SpatialiteNotFound:
diff --git a/tests/test_cli.py b/tests/test_cli.py
index bbc5df30..3fbfdee2 100644
--- a/tests/test_cli.py
+++ b/tests/test_cli.py
@@ -257,6 +257,7 @@ def test_serve_create(ensure_eventloop, tmpdir):
 
 
 def test_serve_duplicate_database_names(ensure_eventloop, tmpdir):
+    "'datasette db.db nested/db.db' should attach two databases, /db and /db_2"
     runner = CliRunner()
     db_1_path = str(tmpdir / "db.db")
     nested = tmpdir / "nested"
@@ -270,6 +271,17 @@ def test_serve_duplicate_database_names(ensure_eventloop, tmpdir):
     assert {db["name"] for db in databases} == {"db", "db_2"}
 
 
+def test_serve_deduplicate_same_database_path(ensure_eventloop, tmpdir):
+    "'datasette db.db db.db' should only attach one database, /db"
+    runner = CliRunner()
+    db_path = str(tmpdir / "db.db")
+    sqlite3.connect(db_path).execute("vacuum")
+    result = runner.invoke(cli, [db_path, db_path, "--get", "/-/databases.json"])
+    assert result.exit_code == 0, result.output
+    databases = json.loads(result.output)
+    assert {db["name"] for db in databases} == {"db"}
+
+
 @pytest.mark.parametrize(
     "filename", ["test-database (1).sqlite", "database (1).sqlite"]
 )