diff --git a/jedi/api/project.py b/jedi/api/project.py
index f39ba90f..d4ef879a 100644
--- a/jedi/api/project.py
+++ b/jedi/api/project.py
@@ -110,7 +110,10 @@ class Project(object):
                 suffixed += discover_buildout_paths(inference_state, inference_state.script_path)
 
                 if add_parent_paths:
-                    traversed = list(traverse_parents(inference_state.script_path))
+                    traversed = list(traverse_parents(
+                        inference_state.script_path,
+                        root=self._path,
+                    ))
 
                     # AFAIK some libraries have imports like `foo.foo.bar`, which
                     # leads to the conclusion to by default prefer longer paths
diff --git a/jedi/common/utils.py b/jedi/common/utils.py
index bc71cafd..2427f7e9 100644
--- a/jedi/common/utils.py
+++ b/jedi/common/utils.py
@@ -2,15 +2,31 @@ import os
 from contextlib import contextmanager
 
 
-def traverse_parents(path, include_current=False):
+def traverse_parents(path, root=None, include_current=False):
+    """Iterate directories from a path to search root
+
+    :path: the path of the script/directory to check.
+    :root: the root of the upward search. Assumes the system root if root is
+            None.
+    :include_current: includes the current file / directory.
+
+    If the root path is not a substring of the provided path, assume the root
+    search path as well.
+    """
     if not include_current:
         path = os.path.dirname(path)
 
     previous = None
-    while previous != path:
-        yield path
-        previous = path
-        path = os.path.dirname(path)
+    if root is None or not path.startswith(root):
+        while previous != path:
+            yield path
+            previous = path
+            path = os.path.dirname(path)
+    else:
+        while previous != root:
+            yield path
+            previous = path
+            path = os.path.dirname(path)
 
 
 @contextmanager