diff --git a/jedi/_compatibility.py b/jedi/_compatibility.py
index c46b6402..8f7bc01f 100644
--- a/jedi/_compatibility.py
+++ b/jedi/_compatibility.py
@@ -85,6 +85,7 @@ def find_module_py33(string, path=None, loader=None, full_name=None, is_global_s
         raise ImportError("Couldn't find a loader for {}".format(string))
 
     return _from_loader(loader, string)
+    issss
     is_package = loader.is_package(string)
     if is_package:
         if hasattr(loader, 'archive'):
@@ -117,11 +118,6 @@ class ZipFileIO(KnownContentFileIO):
 
 def _from_loader(loader, string):
     is_package = loader.is_package(string)
-    #if isinstance(loader, ExtensionLoader):
-        # ExtensionLoader has not attribute get_filename, instead it has a
-        # path attribute that we can use to retrieve the module path
-    #    module_path = loader.path
-    #else:
     try:
         get_filename = loader.get_filename
     except AttributeError:
@@ -129,18 +125,40 @@ def _from_loader(loader, string):
     else:
         module_path = get_filename(string)
 
-    code = loader.get_source(string)
+    # To avoid unicode and read bytes, "overwrite" loader.get_source if
+    # possible.
+    f = loader.get_source.__func__
+    if is_py3 and f is not importlib.machinery.SourceFileLoader.get_source:
+        # Unfortunately we are reading unicode here, not bytes.
+        # It seems hard to get bytes, because the zip importer
+        # logic just unpacks the zip file and returns a file descriptor
+        # that we cannot as easily access. Therefore we just read it as
+        # a string in the cases where get_source was overwritten.
+        code = loader.get_source(string)
+    else:
+        code = _get_source(loader, string)
+
+    if code is None:
+        return None, is_package
     if isinstance(loader, zipimporter):
         return ZipFileIO(module_path, code, loader.archive), is_package
 
-    # Unfortunately we are reading unicode here already, not bytes.
-    # It seems however hard to get bytes, because the zip importer
-    # logic just unpacks the zip file and returns a file descriptor
-    # that we cannot as easily access. Therefore we just read it as
-    # a string.
     return KnownContentFileIO(module_path, code), is_package
 
 
+def _get_source(loader, fullname):
+    """
+    This method is here as a replacement for SourceLoader.get_source. That
+    method returns unicode, but we prefer bytes.
+    """
+    path = loader.get_filename(fullname)
+    try:
+        return loader.get_data(path)
+    except OSError as exc:
+        raise ImportError('source not available through get_data()',
+                          name=fullname) from exc
+
+
 def find_module_pre_py3(string, path=None, full_name=None, is_global_search=True):
     # This import is here, because in other places it will raise a
     # DeprecationWarning.
diff --git a/test/test_api/test_environment.py b/test/test_api/test_environment.py
index cdbe4051..5c1911e4 100644
--- a/test/test_api/test_environment.py
+++ b/test/test_api/test_environment.py
@@ -7,7 +7,8 @@ import jedi
 from jedi._compatibility import py_version
 from jedi.api.environment import get_default_environment, find_virtualenvs, \
     InvalidPythonEnvironment, find_system_environments, \
-    get_system_environment, create_environment, get_cached_default_environment
+    get_system_environment, create_environment, InterpreterEnvironment, \
+    get_cached_default_environment
 
 
 def test_sys_path():
@@ -71,7 +72,9 @@ def test_stdout_in_subprocess(evaluator, Script):
     Script('1').goto_definitions()
 
 
-def test_killed_subprocess(evaluator, Script):
+def test_killed_subprocess(evaluator, Script, environment):
+    if isinstance(environment, InterpreterEnvironment):
+        pytest.skip("We cannot kill our own process")
     # Just kill the subprocess.
     evaluator.compiled_subprocess._compiled_subprocess._process.kill()
     # Since the process was terminated (and nobody knows about it) the first
diff --git a/test/test_evaluate/test_pyc.py b/test/test_evaluate/test_pyc.py
index ac4c6996..37449572 100644
--- a/test/test_evaluate/test_pyc.py
+++ b/test/test_evaluate/test_pyc.py
@@ -13,7 +13,7 @@ import sys
 import pytest
 
 import jedi
-from jedi.api.environment import SameEnvironment
+from jedi.api.environment import SameEnvironment, InterpreterEnvironment
 
 
 SRC = """class Foo:
@@ -55,13 +55,19 @@ def pyc_project_path(tmpdir):
         shutil.rmtree(path)
 
 
-def test_pyc(pyc_project_path):
+def test_pyc(pyc_project_path, environment):
     """
     The list of completion must be greater than 2.
     """
     path = os.path.join(pyc_project_path, 'blub.py')
+    if not isinstance(environment, InterpreterEnvironment):
+        # We are using the same version for pyc completions here, because it
+        # was compiled in that version. However with interpreter environments
+        # we also have the same version and it's easier to debug.
+        environment = SameEnvironment()
+    environment = environment
     s = jedi.Script(
         "from dummy_package import dummy; dummy.",
         path=path,
-        environment=SameEnvironment())
+        environment=environment)
     assert len(s.completions()) >= 2