diff --git a/jedi/api/__init__.py b/jedi/api/__init__.py
index 9e568cf8..86ab8ac4 100644
--- a/jedi/api/__init__.py
+++ b/jedi/api/__init__.py
@@ -32,7 +32,7 @@ from jedi.evaluate import imports
 from jedi.evaluate import usages
 from jedi.evaluate.arguments import try_iter_content
 from jedi.evaluate.helpers import get_module_names, evaluate_call_of_leaf
-from jedi.evaluate.sys_path import dotted_path_in_sys_path
+from jedi.evaluate.sys_path import transform_path_to_dotted
 from jedi.evaluate.filters import TreeNameDefinition, ParamName
 from jedi.evaluate.syntax_tree import tree_name_to_contexts
 from jedi.evaluate.context import ModuleContext
@@ -107,7 +107,6 @@ class Script(object):
         self._evaluator = Evaluator(
             project, environment=environment, script_path=self.path
         )
-        self._project = project
         debug.speed('init')
         self._module_node, source = self._evaluator.parse_and_get_code(
             code=source,
@@ -145,7 +144,7 @@ class Script(object):
     def _get_module(self):
         name = '__main__'
         if self.path is not None:
-            import_names = dotted_path_in_sys_path(self._evaluator.get_sys_path(), self.path)
+            import_names = transform_path_to_dotted(self._evaluator.get_sys_path(), self.path)
             if import_names is not None:
                 name = '.'.join(import_names)
 
diff --git a/jedi/evaluate/imports.py b/jedi/evaluate/imports.py
index 3b1df31a..c7938101 100644
--- a/jedi/evaluate/imports.py
+++ b/jedi/evaluate/imports.py
@@ -559,7 +559,7 @@ def get_modules_containing_name(evaluator, modules, name):
             code = python_bytes_to_unicode(f.read(), errors='replace')
             if name in code:
                 e_sys_path = evaluator.get_sys_path()
-                import_names = sys_path.dotted_path_in_sys_path(e_sys_path, path)
+                import_names = sys_path.transform_path_to_dotted(e_sys_path, path)
                 module = _load_module(
                     evaluator, path, code,
                     sys_path=e_sys_path,
diff --git a/jedi/evaluate/sys_path.py b/jedi/evaluate/sys_path.py
index 8fb1843f..1544acc2 100644
--- a/jedi/evaluate/sys_path.py
+++ b/jedi/evaluate/sys_path.py
@@ -196,30 +196,35 @@ def _get_buildout_script_paths(search_path):
             continue
 
 
-def dotted_path_in_sys_path(sys_path, module_path):
+def transform_path_to_dotted(sys_path, module_path):
     """
-    Returns the dotted path inside a sys.path as a list of names.
+    Returns the dotted path inside a sys.path as a list of names. e.g.
+
+    >>> calculate_dotted_from_path(["/foo"], '/foo/bar/baz.py')
+    ['bar', 'baz']
+
+    Returns None if the path doesn't really resolve to anything.
     """
     # First remove the suffix.
     for suffix in all_suffixes():
         if module_path.endswith(suffix):
             module_path = module_path[:-len(suffix)]
-        break
+            break
     else:
         # There should always be a suffix in a valid Python file on the path.
         return None
 
-    if module_path.startswith(os.path.sep):
-        # The paths in sys.path most of the times don't end with a slash.
-        module_path = module_path[1:]
-
     for p in sys_path:
         if module_path.startswith(p):
             rest = module_path[len(p):]
+            if rest.startswith(os.path.sep):
+                # Remove a slash in cases it's still there.
+                rest = rest[1:]
+
             if rest:
                 split = rest.split(os.path.sep)
                 for string in split:
-                    if not string or '.' in string:
+                    if not string:
                         return None
                 return split
 
diff --git a/test/test_evaluate/test_sys_path.py b/test/test_evaluate/test_sys_path.py
index dab4f471..a43e5262 100644
--- a/test/test_evaluate/test_sys_path.py
+++ b/test/test_evaluate/test_sys_path.py
@@ -3,6 +3,8 @@ from glob import glob
 import sys
 import shutil
 
+import pytest
+
 from jedi.evaluate import sys_path
 from jedi.api.environment import create_environment
 
@@ -59,3 +61,29 @@ def test_venv_and_pths(venv_path):
 
     # Ensure that none of venv dirs leaked to the interpreter.
     assert not set(sys.path).intersection(ETALON)
+
+
+_s = ['/a', '/b', '/c/d/']
+
+
+@pytest.mark.parametrize(
+    'sys_path_, module_path, result', [
+        (_s, '/a/b', None),
+        (_s, '/a/b/c', None),
+        (_s, '/a/b.py', ['b']),
+        (_s, '/a/b/c.py', ['b', 'c']),
+        (_s, '/x/b.py', None),
+        (_s, '/c/d/x.py', ['x']),
+        (_s, '/c/d/x.py', ['x']),
+        (_s, '/c/d/x/y.py', ['x', 'y']),
+        # If dots are in there they also resolve. These are obviously illegal
+        # in Python, but Jedi can handle them. Give the user a bit more freedom
+        # that he will have to correct eventually.
+        (_s, '/a/b.c.py', ['b.c']),
+        (_s, '/a/b.d/foo.bar.py', ['b.d', 'foo.bar']),
+
+        (_s, '/a/.py', None),
+        (_s, '/a/c/.py', None),
+    ])
+def test_calculate_dotted_from_path(sys_path_, module_path, result):
+    assert sys_path.transform_path_to_dotted(sys_path_, module_path) == result