diff --git a/HISTORY.rst b/HISTORY.rst
index 57ecc7f660..c199dc10d8 100644
--- a/HISTORY.rst
+++ b/HISTORY.rst
@@ -1,5 +1,5 @@
-3.1.5 (2018-10-7)
-=================
+3.1.5 (2018-10-08)
+==================
 * Consolidate some document indexing test code into a new mixin.
 * Split the code of the mountindex command to be able to add tests.
 * Fix the way the children of IndexInstanceNode are accessed. Fixes GitLab
@@ -31,9 +31,12 @@
   Thanks to TheOneValen @TheOneValen for the report.
 * Add shared cache class and add mounted index cache invalidation when
   document and index instance nodes are updated or deleted.
+* Fix document metadata app view error when adding multiple optional
+  metadata types. Closes GitLab issue #521. Thanks to the TheOneValen
+  @TheOneValen for the report.
 
-3.1.4 (2018-10-4)
-=================
+3.1.4 (2018-10-04)
+==================
 * Fix the link to the documenation. Closes GitLab issue #516.
   Thanks to Matthias Urlichs @smurfix for the report.
 * Update related links. Add links to the new Wiki and Forum.
diff --git a/docs/releases/3.1.5.rst b/docs/releases/3.1.5.rst
index 66d8a617f6..a931043364 100644
--- a/docs/releases/3.1.5.rst
+++ b/docs/releases/3.1.5.rst
@@ -2,7 +2,7 @@
 Mayan EDMS v3.1.5 release notes
 ===============================
 
-Released: October 7, 2018
+Released: October 8, 2018
 
 Index mirroring fixes
 ~~~~~~~~~~~~~~~~~~~~~
@@ -59,6 +59,9 @@ Other changes
   Thanks to TheOneValen @TheOneValen for the report.
 * Add shared cache class and add mounted index cache invalidation when
   document and index instance nodes are updated or deleted.
+* Fix document metadata app view error when adding multiple optional
+  metadata types. Closes GitLab issue #521. Thanks to the TheOneValen
+  @TheOneValen for the report.
 
 Removals
 --------
@@ -128,5 +131,6 @@ Bugs fixed or issues closed
 
 * `GitLab issue #518 <https://gitlab.com/mayan-edms/mayan-edms/issues/518>`_ mountindex broken (3.1.x)
 * `GitLab issue #519 <https://gitlab.com/mayan-edms/mayan-edms/issues/519>`_ Mail body fetched despite setting not to
+* `GitLab issue #521 <https://gitlab.com/mayan-edms/mayan-edms/issues/521>`_ Adding multiple metadata at once fails
 
 .. _PyPI: https://pypi.python.org/pypi/mayan-edms/
diff --git a/mayan/apps/metadata/tests/test_views.py b/mayan/apps/metadata/tests/test_views.py
index 703a2614e6..db88b27fe4 100644
--- a/mayan/apps/metadata/tests/test_views.py
+++ b/mayan/apps/metadata/tests/test_views.py
@@ -303,6 +303,35 @@ class DocumentMetadataTestCase(GenericDocumentViewTestCase):
 
         self.assertContains(response, 'Edit', status_code=200)
 
+    def test_single_document_multiple_metadata_add_view(self):
+        self.login_user()
+
+        self.grant_permission(permission=permission_document_view)
+        self.grant_permission(permission=permission_metadata_document_add)
+        self.grant_permission(permission=permission_metadata_document_edit)
+
+        metadata_type_2 = MetadataType.objects.create(
+            name=TEST_METADATA_TYPE_NAME_2, label=TEST_METADATA_TYPE_LABEL_2
+        )
+
+        self.document_type.metadata.create(
+            metadata_type=metadata_type_2
+        )
+
+        response = self.post(
+            'metadata:metadata_add', args=(self.document.pk,), data={
+                'metadata_type': [self.metadata_type.pk, metadata_type_2.pk],
+            }
+        )
+
+        document_metadata_types = self.document.metadata.values_list(
+            'metadata_type', flat=True
+        )
+        self.assertTrue(
+            self.metadata_type.pk in document_metadata_types and
+            metadata_type_2.pk in document_metadata_types
+        )
+
 
 class MetadataTypeViewTestCase(DocumentTestMixin, MetadataTestsMixin, GenericViewTestCase):
     auto_create_document_type = False
diff --git a/mayan/apps/metadata/views.py b/mayan/apps/metadata/views.py
index 0fdcb222fa..f88ebdfe1f 100644
--- a/mayan/apps/metadata/views.py
+++ b/mayan/apps/metadata/views.py
@@ -161,13 +161,13 @@ class DocumentMetadataAddView(MultipleObjectFormActionView):
                         metadata_type=metadata_type,
                     )
                 except DocumentMetadata.DoesNotExist:
-                    instance = DocumentMetadata(
+                    document_metadata = DocumentMetadata(
                         document=instance,
                         metadata_type=metadata_type,
                     )
-                    instance.save(_user=self.request.user)
+                    document_metadata.save(_user=self.request.user)
                     created = True
-            except ValidationError as exception:
+            except Exception as exception:
                 messages.error(
                     self.request,
                     _(