diff --git a/google/cloud/storage/blob.py b/google/cloud/storage/blob.py
index 93beced90..dcf7d031e 100644
--- a/google/cloud/storage/blob.py
+++ b/google/cloud/storage/blob.py
@@ -1986,9 +1986,10 @@ def metadata(self, value):
         See https://cloud.google.com/storage/docs/json_api/v1/objects
 
         :type value: dict
-        :param value: (Optional) The blob metadata to set.
+        :param value: The blob metadata to set.
         """
-        value = {k: str(v) for k, v in value.items()}
+        if value is not None:
+            value = {k: str(v) for k, v in value.items()}
         self._patch_property("metadata", value)
 
     @property
diff --git a/tests/unit/test_blob.py b/tests/unit/test_blob.py
index 1c2b1e90d..5246d3716 100644
--- a/tests/unit/test_blob.py
+++ b/tests/unit/test_blob.py
@@ -1215,6 +1215,16 @@ def test__get_writable_metadata_unwritable_field(self):
         expected = {"name": name}
         self.assertEqual(object_metadata, expected)
 
+    def test__set_metadata_to_none(self):
+        name = u"blob-name"
+        blob = self._make_one(name, bucket=None)
+        blob.storage_class = "NEARLINE"
+        blob.cache_control = "max-age=3600"
+
+        with mock.patch("google.cloud.storage.blob.Blob._patch_property") as patch_prop:
+            blob.metadata = None
+            patch_prop.assert_called_once_with("metadata", None)
+
     def test__get_upload_arguments(self):
         name = u"blob-name"
         key = b"[pXw@,p@@AfBfrR3x-2b2SCHR,.?YwRO"