diff --git a/importlib_resources/_py3.py b/importlib_resources/_py3.py
index a2647f481fef211..4687d98f31100e7 100644
--- a/importlib_resources/_py3.py
+++ b/importlib_resources/_py3.py
@@ -4,7 +4,7 @@
 
 from . import abc as resources_abc
 from builtins import open as builtins_open
-from contextlib import contextmanager
+from contextlib import contextmanager, suppress
 from importlib import import_module
 from importlib.abc import ResourceLoader
 from io import BytesIO, TextIOWrapper
@@ -78,9 +78,11 @@ def open_binary(package: Package, resource: Resource) -> BinaryIO:
         # importlib.machinery loaders are and an AttributeError for
         # get_data() will make it clear what is needed from the loader.
         loader = cast(ResourceLoader, package.__spec__.loader)
-        try:
-            data = loader.get_data(full_path)
-        except IOError:
+        data = None
+        if hasattr(package.__spec__.loader, 'get_data'):
+            with suppress(IOError):
+                data = loader.get_data(full_path)
+        if data is None:
             package_name = package.__spec__.name
             message = '{!r} resource not found in {!r}'.format(
                 resource, package_name)
@@ -112,9 +114,11 @@ def open_text(package: Package,
         # importlib.machinery loaders are and an AttributeError for
         # get_data() will make it clear what is needed from the loader.
         loader = cast(ResourceLoader, package.__spec__.loader)
-        try:
-            data = loader.get_data(full_path)
-        except IOError:
+        data = None
+        if hasattr(package.__spec__.loader, 'get_data'):
+            with suppress(IOError):
+                data = loader.get_data(full_path)
+        if data is None:
             package_name = package.__spec__.name
             message = '{!r} resource not found in {!r}'.format(
                 resource, package_name)
@@ -255,6 +259,11 @@ def contents(package: Package) -> Iterator[str]:
     if reader is not None:
         yield from reader.contents()
         return
+    # Is the package a namespace package?  By definition, namespace packages
+    # cannot have resources.
+    if (package.__spec__.origin == 'namespace' and
+            not package.__spec__.has_location):
+        return []
     package_directory = Path(package.__spec__.origin).parent
     try:
         yield from os.listdir(str(package_directory))
diff --git a/importlib_resources/docs/changelog.rst b/importlib_resources/docs/changelog.rst
index 05982ae7c503264..04489d531e0ee99 100644
--- a/importlib_resources/docs/changelog.rst
+++ b/importlib_resources/docs/changelog.rst
@@ -9,6 +9,7 @@
   ``open_text()``, ``read_binary()``, and ``read_text()``.  Closes #41
 * Fix a bug where unrelated resources could be returned from ``contents()``.
   Closes #44
+* Correctly prevent namespace packages from containing resources.  Closes #20
 
 
 0.1 (2017-12-05)
diff --git a/importlib_resources/tests/data03/__init__.py b/importlib_resources/tests/data03/__init__.py
new file mode 100644
index 000000000000000..e69de29bb2d1d64
diff --git a/importlib_resources/tests/data03/namespace/portion1/__init__.py b/importlib_resources/tests/data03/namespace/portion1/__init__.py
new file mode 100644
index 000000000000000..e69de29bb2d1d64
diff --git a/importlib_resources/tests/data03/namespace/portion2/__init__.py b/importlib_resources/tests/data03/namespace/portion2/__init__.py
new file mode 100644
index 000000000000000..e69de29bb2d1d64
diff --git a/importlib_resources/tests/data03/namespace/resource1.txt b/importlib_resources/tests/data03/namespace/resource1.txt
new file mode 100644
index 000000000000000..e69de29bb2d1d64
diff --git a/importlib_resources/tests/test_resource.py b/importlib_resources/tests/test_resource.py
index 6d46c92ce4f0ef2..93d0800f7554404 100644
--- a/importlib_resources/tests/test_resource.py
+++ b/importlib_resources/tests/test_resource.py
@@ -111,5 +111,35 @@ def test_unrelated_contents(self):
             {'__init__.py', 'resource2.txt'})
 
 
+@unittest.skipIf(sys.version_info < (3,), 'No namespace packages in Python 2')
+class NamespaceTest(unittest.TestCase):
+    def test_namespaces_cant_have_resources(self):
+        contents = set(resources.contents(
+            'importlib_resources.tests.data03.namespace'))
+        self.assertEqual(len(contents), 0)
+        # Even though there is a file in the namespace directory, it is not
+        # considered a resource, since namespace packages can't have them.
+        self.assertFalse(resources.is_resource(
+            'importlib_resources.tests.data03.namespace',
+            'resource1.txt'))
+        # We should get an exception if we try to read it or open it.
+        self.assertRaises(
+            FileNotFoundError,
+            resources.open_text,
+            'importlib_resources.tests.data03.namespace', 'resource1.txt')
+        self.assertRaises(
+            FileNotFoundError,
+            resources.open_binary,
+            'importlib_resources.tests.data03.namespace', 'resource1.txt')
+        self.assertRaises(
+            FileNotFoundError,
+            resources.read_text,
+            'importlib_resources.tests.data03.namespace', 'resource1.txt')
+        self.assertRaises(
+            FileNotFoundError,
+            resources.read_binary,
+            'importlib_resources.tests.data03.namespace', 'resource1.txt')
+
+
 if __name__ == '__main__':
     unittest.main()