diff --git a/mayan/apps/metadata/models.py b/mayan/apps/metadata/models.py
index b73100878b..38d8c53214 100644
--- a/mayan/apps/metadata/models.py
+++ b/mayan/apps/metadata/models.py
@@ -65,6 +65,7 @@ class DocumentMetadata(models.Model):
         return super(DocumentMetadata, self).delete(*args, **kwargs)
 
     class Meta:
+        unique_together = ('document', 'metadata_type')
         verbose_name = _(u'Document metadata')
         verbose_name_plural = _(u'Document metadata')
 
diff --git a/mayan/apps/metadata/south_migrations/0010_auto__add_unique_documentmetadata_document_metadata_type.py b/mayan/apps/metadata/south_migrations/0010_auto__add_unique_documentmetadata_document_metadata_type.py
new file mode 100644
index 0000000000..289d5c53be
--- /dev/null
+++ b/mayan/apps/metadata/south_migrations/0010_auto__add_unique_documentmetadata_document_metadata_type.py
@@ -0,0 +1,61 @@
+# -*- coding: utf-8 -*-
+from south.utils import datetime_utils as datetime
+from south.db import db
+from south.v2 import SchemaMigration
+from django.db import models
+
+
+class Migration(SchemaMigration):
+
+    def forwards(self, orm):
+        # Adding unique constraint on 'DocumentMetadata', fields ['document', 'metadata_type']
+        db.create_unique(u'metadata_documentmetadata', ['document_id', 'metadata_type_id'])
+
+
+    def backwards(self, orm):
+        # Removing unique constraint on 'DocumentMetadata', fields ['document', 'metadata_type']
+        db.delete_unique(u'metadata_documentmetadata', ['document_id', 'metadata_type_id'])
+
+
+    models = {
+        u'documents.document': {
+            'Meta': {'ordering': "['-date_added']", 'object_name': 'Document'},
+            'date_added': ('django.db.models.fields.DateTimeField', [], {'auto_now_add': 'True', 'blank': 'True'}),
+            'description': ('django.db.models.fields.TextField', [], {'null': 'True', 'blank': 'True'}),
+            'document_type': ('django.db.models.fields.related.ForeignKey', [], {'related_name': "'documents'", 'to': u"orm['documents.DocumentType']"}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'label': ('django.db.models.fields.CharField', [], {'default': "u'Uninitialized document'", 'max_length': '255', 'db_index': 'True'}),
+            'language': ('django.db.models.fields.CharField', [], {'default': "u'eng'", 'max_length': '8'}),
+            'uuid': ('django.db.models.fields.CharField', [], {'default': "u'd55c3d30-544c-4ac2-90ac-112f4a4e235a'", 'max_length': '48'})
+        },
+        u'documents.documenttype': {
+            'Meta': {'ordering': "['name']", 'object_name': 'DocumentType'},
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'name': ('django.db.models.fields.CharField', [], {'unique': 'True', 'max_length': '32'}),
+            'ocr': ('django.db.models.fields.BooleanField', [], {'default': 'True'})
+        },
+        u'metadata.documentmetadata': {
+            'Meta': {'unique_together': "(('document', 'metadata_type'),)", 'object_name': 'DocumentMetadata'},
+            'document': ('django.db.models.fields.related.ForeignKey', [], {'related_name': "'document_metadata'", 'to': u"orm['documents.Document']"}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'metadata_type': ('django.db.models.fields.related.ForeignKey', [], {'to': u"orm['metadata.MetadataType']"}),
+            'value': ('django.db.models.fields.CharField', [], {'db_index': 'True', 'max_length': '255', 'null': 'True', 'blank': 'True'})
+        },
+        u'metadata.documenttypemetadatatype': {
+            'Meta': {'unique_together': "(('document_type', 'metadata_type'),)", 'object_name': 'DocumentTypeMetadataType'},
+            'document_type': ('django.db.models.fields.related.ForeignKey', [], {'to': u"orm['documents.DocumentType']"}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'metadata_type': ('django.db.models.fields.related.ForeignKey', [], {'to': u"orm['metadata.MetadataType']"}),
+            'required': ('django.db.models.fields.BooleanField', [], {'default': 'False'})
+        },
+        u'metadata.metadatatype': {
+            'Meta': {'ordering': "('title',)", 'object_name': 'MetadataType'},
+            'default': ('django.db.models.fields.CharField', [], {'max_length': '128', 'null': 'True', 'blank': 'True'}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'lookup': ('django.db.models.fields.TextField', [], {'null': 'True', 'blank': 'True'}),
+            'name': ('django.db.models.fields.CharField', [], {'unique': 'True', 'max_length': '48'}),
+            'title': ('django.db.models.fields.CharField', [], {'max_length': '48'})
+        }
+    }
+
+    complete_apps = ['metadata']
\ No newline at end of file