diff --git a/_pytest/main.py b/_pytest/main.py
index 3bd4022b7..eacae8dab 100644
--- a/_pytest/main.py
+++ b/_pytest/main.py
@@ -521,8 +521,16 @@ class FSCollector(Collector):
         super(FSCollector, self).__init__(name, parent, config, session)
         self.fspath = fspath
 
+    def _check_initialpaths_for_relpath(self):
+        for initialpath in self.session._initialpaths:
+            if self.fspath.common(initialpath) == initialpath:
+                return self.fspath.relto(initialpath.dirname)
+
     def _makeid(self):
         relpath = self.fspath.relto(self.config.rootdir)
+
+        if not relpath:
+            relpath = self._check_initialpaths_for_relpath()
         if os.sep != nodes.SEP:
             relpath = relpath.replace(os.sep, nodes.SEP)
         return relpath
diff --git a/changelog/2775.bugfix b/changelog/2775.bugfix
new file mode 100644
index 000000000..8123522ac
--- /dev/null
+++ b/changelog/2775.bugfix
@@ -0,0 +1 @@
+Fix the bug where running pytest with "--pyargs" will result in Items with empty "parent.nodeid" if run from a different root directory.
diff --git a/testing/acceptance_test.py b/testing/acceptance_test.py
index 712776906..8a8c32762 100644
--- a/testing/acceptance_test.py
+++ b/testing/acceptance_test.py
@@ -624,8 +624,10 @@ class TestInvocationVariants(object):
         for p in search_path:
             monkeypatch.syspath_prepend(p)
 
+        os.chdir('world')
         # mixed module and filenames:
-        result = testdir.runpytest("--pyargs", "-v", "ns_pkg.hello", "world/ns_pkg")
+        result = testdir.runpytest("--pyargs", "-v", "ns_pkg.hello", "ns_pkg/world")
+        testdir.chdir()
         assert result.ret == 0
         result.stdout.fnmatch_lines([
             "*test_hello.py::test_hello*PASSED",