diff --git a/datasette/app.py b/datasette/app.py
index 98a31364..34300272 100644
--- a/datasette/app.py
+++ b/datasette/app.py
@@ -227,7 +227,7 @@ class Datasette:
         self.databases.pop(name)
 
     def scan_dirs(self):
-        # Recurse through self.dirs looking for new SQLite DBs
+        # Recurse through self.dirs looking for new SQLite DBs. Runs in a thread.
         while True:
             current_filepaths = {
                 d.path for d in list(self.databases.values()) if d.path is not None
diff --git a/datasette/utils/__init__.py b/datasette/utils/__init__.py
index c15b7eae..f0a2cb89 100644
--- a/datasette/utils/__init__.py
+++ b/datasette/utils/__init__.py
@@ -603,7 +603,8 @@ def is_valid_sqlite(path):
         return False
     # Check we can run `select * from sqlite_master`
     try:
-        sqlite3.connect(str(path)).execute("select * from sqlite_master")
+        conn = sqlite3.connect(str(path))
+        check_connection(conn)
     except Exception:
         return False
     return True