diff --git a/jedi/inference/imports.py b/jedi/inference/imports.py
index c1a4953f..f7a363c1 100644
--- a/jedi/inference/imports.py
+++ b/jedi/inference/imports.py
@@ -480,7 +480,7 @@ def _load_builtin_module(inference_state, import_names=None, sys_path=None):
     if sys_path is None:
         sys_path = inference_state.get_sys_path()
     if not project._load_unsafe_extensions:
-        safe_paths = project._get_base_sys_path(inference_state)
+        safe_paths = set(project._get_base_sys_path(inference_state))
         sys_path = [p for p in sys_path if p in safe_paths]
 
     dotted_name = '.'.join(import_names)