diff --git a/_pytest/main.py b/_pytest/main.py
index 76a4fc128e9..2f2d6c26f2c 100644
--- a/_pytest/main.py
+++ b/_pytest/main.py
@@ -655,9 +655,12 @@ def _tryconvertpyarg(self, x):
             return x
         if loader is None:
             return x
+        # This method is sometimes invoked when AssertionRewritingHook, which
+        # does not define a get_filename method, is already in place:
         try:
             path = loader.get_filename()
-        except:
+        except AttributeError:
+            # Retrieve path from AssertionRewritingHook:
             path = loader.modules[x][0].co_filename
         if loader.is_package(x):
             path = os.path.dirname(path)
diff --git a/testing/acceptance_test.py b/testing/acceptance_test.py
index c66a1740f11..91854367e51 100644
--- a/testing/acceptance_test.py
+++ b/testing/acceptance_test.py
@@ -1,4 +1,5 @@
 # -*- coding: utf-8 -*-
+import os
 import sys
 
 import _pytest._code
@@ -513,22 +514,12 @@ def test_pyargs_importerror(self, testdir, monkeypatch):
         path = testdir.mkpydir("tpkg")
         path.join("test_hello.py").write('raise ImportError')
 
-        result = testdir.runpytest("--pyargs", "tpkg.test_hello")
+        result = testdir.runpytest_subprocess("--pyargs", "tpkg.test_hello")
         assert result.ret != 0
 
-        # Depending on whether the process running the test is the
-        # same as the process parsing the command-line arguments, the
-        # type of failure can be different:
-        if result.stderr.str() == '':
-            # Different processes
-            result.stdout.fnmatch_lines([
-                "collected*0*items*/*1*errors"
-            ])
-        else:
-            # Same process
-            result.stderr.fnmatch_lines([
-                "ERROR:*file*or*package*not*found:*tpkg.test_hello"
-            ])
+        result.stdout.fnmatch_lines([
+            "collected*0*items*/*1*errors"
+        ])
 
     def test_cmdline_python_package(self, testdir, monkeypatch):
         monkeypatch.delenv('PYTHONDONTWRITEBYTECODE', False)
@@ -605,7 +596,7 @@ def join_pythonpath(*dirs):
             cur = py.std.os.environ.get('PYTHONPATH')
             if cur:
                 dirs += (cur,)
-            return ':'.join(str(p) for p in dirs)
+            return os.pathsep.join(str(p) for p in dirs)
         monkeypatch.setenv('PYTHONPATH', join_pythonpath(*search_path))
         for p in search_path:
             monkeypatch.syspath_prepend(p)