diff --git a/src/octoprint/plugin/core.py b/src/octoprint/plugin/core.py
index f8a168f5..4f98a29a 100644
--- a/src/octoprint/plugin/core.py
+++ b/src/octoprint/plugin/core.py
@@ -571,6 +571,10 @@ class PluginManager(object):
 					key = entry.name
 				elif entry.is_file() and entry.name.endswith(".py"):
 					key = entry.name[:-3] # strip off the .py extension
+					if key.startswith("__"):
+						# might be an __init__.py in our plugins folder, or something else we don't want
+						# to handle
+						continue
 				else:
 					continue
 
diff --git a/src/octoprint/plugins/__init__.py b/src/octoprint/plugins/__init__.py
new file mode 100644
index 00000000..1b0510c6
--- /dev/null
+++ b/src/octoprint/plugins/__init__.py
@@ -0,0 +1 @@
+# make our plugins testable
diff --git a/src/octoprint/plugins/pluginmanager/__init__.py b/src/octoprint/plugins/pluginmanager/__init__.py
index 8f31b101..05985833 100644
--- a/src/octoprint/plugins/pluginmanager/__init__.py
+++ b/src/octoprint/plugins/pluginmanager/__init__.py
@@ -808,20 +808,37 @@ class PluginManagerPlugin(octoprint.plugin.SimpleApiPlugin,
 
 		return True
 
-	def _is_os_compatible(self, current_os, compatibility_entries):
+	@staticmethod
+	def _is_os_compatible(current_os, compatibility_entries):
 		"""
-		Tests if the ``current_os`` or ``sys.platform`` matches any of the provided ``compatibility_entries``.
+		Tests if the ``current_os`` or ``sys.platform`` are blacklisted or whitelisted in ``compatibility_entries``
 		"""
-		general_match = current_os in filter(lambda x: x in self.__class__.OPERATING_SYSTEMS.keys(), compatibility_entries)
-		exact_match = sys.platform in compatibility_entries
-		return general_match or exact_match
+		if len(compatibility_entries) == 0:
+			# shortcut - no compatibility info means we are compatible
+			return True
 
-	def _get_os(self):
-		for identifier, platforms in self.__class__.OPERATING_SYSTEMS.items():
+		negative_entries = map(lambda x: x[1:], filter(lambda x: x.startswith("!"), compatibility_entries))
+		positive_entries = filter(lambda x: not x.startswith("!"), compatibility_entries)
+
+		negative_match = False
+		if negative_entries:
+			# check if we are blacklisted
+			negative_match = current_os in negative_entries or any(map(lambda x: sys.platform.startswith(x), negative_entries))
+
+		positive_match = True
+		if positive_entries:
+			# check if we are whitelisted
+			positive_match = current_os in positive_entries or any(map(lambda x: sys.platform.startswith(x), positive_entries))
+
+		return positive_match and not negative_match
+
+	@classmethod
+	def _get_os(cls):
+		for identifier, platforms in cls.OPERATING_SYSTEMS.items():
 			if (callable(platforms) and platforms(sys.platform)) or (isinstance(platforms, list) and sys.platform in platforms):
 				return identifier
 		else:
-			return "unknown"
+			return "unmapped"
 
 	def _get_octoprint_version_string(self):
 		return VERSION
diff --git a/tests/plugins/__init__.py b/tests/plugins/__init__.py
new file mode 100644
index 00000000..858aac82
--- /dev/null
+++ b/tests/plugins/__init__.py
@@ -0,0 +1,10 @@
+# coding=utf-8
+"""
+Unit tests for bundled plugins.
+"""
+
+from __future__ import absolute_import
+
+__author__ = "Gina Häußge <osd@foosel.net>"
+__license__ = 'GNU Affero General Public License http://www.gnu.org/licenses/agpl.html'
+__copyright__ = "Copyright (C) 2017 The OctoPrint Project - Released under terms of the AGPLv3 License"
diff --git a/tests/plugins/test_pluginmanager.py b/tests/plugins/test_pluginmanager.py
new file mode 100644
index 00000000..28194c85
--- /dev/null
+++ b/tests/plugins/test_pluginmanager.py
@@ -0,0 +1,61 @@
+# coding=utf-8
+"""
+Unit tests for bundled plugin "PluginManager".
+"""
+
+from __future__ import absolute_import
+
+__author__ = "Gina Häußge <osd@foosel.net>"
+__license__ = 'GNU Affero General Public License http://www.gnu.org/licenses/agpl.html'
+__copyright__ = "Copyright (C) 2017 The OctoPrint Project - Released under terms of the AGPLv3 License"
+
+import unittest
+import mock
+import ddt
+
+from octoprint.plugins.pluginmanager import PluginManagerPlugin
+
+@ddt.ddt
+class PluginManagerPluginTests(unittest.TestCase):
+
+	@ddt.data(
+		("linux", "linux2", [], True),
+		("linux", "linux2", ["linux", "freebsd"], True),
+		("windows", "win32", ["linux", "freebsd"], False),
+		("linux", "linux2", ["!windows"], True),
+		("windows", "win32", ["!windows"], False),
+		("unmapped", "os2", [], True),
+		("unmapped", "os2", ["linux", "freebsd"], False),
+		("unmapped", "os2", ["!os2"], False),
+		("unmapped", "sunos5", ["linux", "freebsd", "sunos"], True),
+		("unmapped", "sunos5", ["!sunos", "!os2"], False),
+
+		# both black and white listing at the same time usually doesn't
+		# make a whole lot of sense, but let's test it anyhow
+		("linux", "linux2", ["!windows", "linux", "freebsd"], True),
+		("linux", "linux2", ["!windows", "freebsd"], False),
+		("windows", "win32", ["!windows", "linux", "freebsd"], False),
+		("unmapped", "sunos5", ["!windows", "linux", "freebsd"], False)
+	)
+	@ddt.unpack
+	def test_is_os_compatible(self, current_os, sys_platform, entries, expected):
+		with mock.patch("sys.platform", sys_platform):
+			actual = PluginManagerPlugin._is_os_compatible(current_os, entries)
+			self.assertEqual(actual, expected)
+
+	@ddt.data(
+		("win32", "windows"),
+		("linux2", "linux"),
+		("darwin", "macos"),
+		("linux", "linux"),
+		("linux3", "linux"),
+		("freebsd", "freebsd"),
+		("freebsd2342", "freebsd"),
+		("os2", "unmapped"),
+		("sunos5", "unmapped")
+	)
+	@ddt.unpack
+	def test_get_os(self, sys_platform, expected):
+		with mock.patch("sys.platform", sys_platform):
+			actual = PluginManagerPlugin._get_os()
+			self.assertEqual(actual, expected)