diff --git a/src/zeep/xsd/types/builtins.py b/src/zeep/xsd/types/builtins.py
index 56f28da6..2e720cd7 100644
--- a/src/zeep/xsd/types/builtins.py
+++ b/src/zeep/xsd/types/builtins.py
@@ -149,6 +149,12 @@ def xmlvalue(self, value):
         if isinstance(value, str):
             return value
 
+        if not isinstance(value, datetime.datetime):
+            # The value passed in could be either a datetime or a date
+            # if it's a date merge in datetime.time.min - `datetime.time(0, 0)`
+            # to make it a datetime
+            value = datetime.datetime.combine(value, datetime.time.min)
+
         return value.isoformat().replace("+00:00", "Z")
 
     @treat_whitespace("collapse")
@@ -188,6 +194,7 @@ class Date(BuiltinType):
     def xmlvalue(self, value):
         if isinstance(value, str):
             return value
+
         return value.strftime("%Y-%m-%d")
 
     @treat_whitespace("collapse")
diff --git a/tests/test_xsd_builtins.py b/tests/test_xsd_builtins.py
index 4f055da9..4d209c10 100644
--- a/tests/test_xsd_builtins.py
+++ b/tests/test_xsd_builtins.py
@@ -156,6 +156,10 @@ def test_pythonvalue(self):
 
 class TestDateTime:
     def test_xmlvalue(self):
+        instance = builtins.DateTime()
+        value = datetime.date(2016, 3, 4)
+        assert instance.xmlvalue(value) == "2016-03-04T00:00:00"
+
         instance = builtins.DateTime()
         value = datetime.datetime(2016, 3, 4, 21, 14, 42)
         assert instance.xmlvalue(value) == "2016-03-04T21:14:42"