diff --git a/stix2/observables.py b/stix2/observables.py
index bb4ea31..9c1b368 100644
--- a/stix2/observables.py
+++ b/stix2/observables.py
@@ -110,11 +110,9 @@ class EmailMessage(_Observable):
     def _check_object_constraints(self):
         super(EmailMessage, self)._check_object_constraints()
         self._check_properties_dependency(["is_multipart"], ["body_multipart"])
-        if self.get("is_multipart") is False and self.get("body"):
-            raise DependentPropertiesError(
-                self.__class__,
-                (self.get("is_multipart"), self.get("body"))
-            )
+        if self.get("is_multipart") is True and self.get("body"):
+            # 'body' MAY only be used if is_multipart is false.
+            raise DependentPropertiesError(self.__class__, [("is_multipart", "body")])
 
 
 class ArchiveExt(_Extension):
@@ -447,13 +445,13 @@ class Process(_Observable):
         super(Process, self)._check_object_constraints()
         try:
             self._check_at_least_one_property()
-            if "windows-process-ext" in self.get("extensions", []):
+            if "windows-process-ext" in self.get('extensions', {}):
                 self.extensions["windows-process-ext"]._check_at_least_one_property()
         except AtLeastOnePropertyError as enclosing_exc:
-            if not hasattr(self, 'extensions'):
+            if 'extensions' not in self:
                 raise enclosing_exc
             else:
-                if "windows-process-ext" in self.get("extensions", []):
+                if "windows-process-ext" in self.get('extensions', {}):
                     self.extensions["windows-process-ext"]._check_at_least_one_property()
 
 
diff --git a/stix2/test/test_observed_data.py b/stix2/test/test_observed_data.py
index b934b31..0ed9954 100644
--- a/stix2/test/test_observed_data.py
+++ b/stix2/test/test_observed_data.py
@@ -294,6 +294,31 @@ def test_parse_email_message(data):
     assert odata.body_multipart[0].content_disposition == "inline"
 
 
+@pytest.mark.parametrize("data", [
+    """
+    {
+         "type": "email-message",
+         "from_ref": "0",
+         "to_refs": ["1"],
+         "is_multipart": true,
+         "date": "1997-11-21T15:55:06.000Z",
+         "subject": "Saying Hello",
+         "body": "Cats are funny!"
+    }
+    """
+])
+def test_parse_email_message_not_multipart(data):
+    valid_refs = {
+        "0": "email-addr",
+        "1": "email-addr",
+    }
+    with pytest.raises(stix2.exceptions.DependentPropertiesError) as excinfo:
+        stix2.parse_observable(data, valid_refs)
+
+    assert excinfo.value.cls == stix2.EmailMessage
+    assert excinfo.value.dependencies == [("is_multipart", "body")]
+
+
 @pytest.mark.parametrize("data", [
     """"0": {
             "type": "file",
@@ -913,6 +938,23 @@ def test_process_example_empty_with_extensions():
     assert excinfo.value.properties == sorted(properties_of_extension)
 
 
+def test_process_example_windows_process_ext():
+    proc = stix2.Process(pid=314,
+                         name="foobar.exe",
+                         extensions={
+                             "windows-process-ext": {
+                                 "aslr_enabled": True,
+                                 "dep_enabled": True,
+                                 "priority": "HIGH_PRIORITY_CLASS",
+                                 "owner_sid": "S-1-5-21-186985262-1144665072-74031268-1309"
+                             }
+                         })
+    assert proc.extensions["windows-process-ext"].aslr_enabled
+    assert proc.extensions["windows-process-ext"].dep_enabled
+    assert proc.extensions["windows-process-ext"].priority == "HIGH_PRIORITY_CLASS"
+    assert proc.extensions["windows-process-ext"].owner_sid == "S-1-5-21-186985262-1144665072-74031268-1309"
+
+
 def test_process_example_windows_process_ext_empty():
     with pytest.raises(stix2.exceptions.AtLeastOnePropertyError) as excinfo:
             stix2.Process(pid=1221,