diff --git a/articles/models.py b/articles/models.py
index 816ea8b..e044ff6 100644
--- a/articles/models.py
+++ b/articles/models.py
@@ -11,7 +11,7 @@ from tagulous.models import TagField
 class Category(models.Model):
     title = models.CharField(max_length=40, unique=True)
     slug = models.SlugField(max_length=40, unique=True)
-    introduction = models.TextField(blank=True, null=True)
+    introduction = models.TextField(blank=True)
 
     def save(self, force_insert=False, force_update=False, using=None, update_fields=None):
         if not self.slug:
@@ -33,9 +33,9 @@ class Article(models.Model):
     subtitle = models.CharField(max_length=200, blank=True, null=True)
     slug = models.SlugField(max_length=200, unique=True)
     category = models.ForeignKey(Category, on_delete=models.PROTECT, related_name='articles')
-    introduction = models.TextField(blank=True, null=True)
+    introduction = models.TextField(blank=True)
     body = MarkdownxField()
-    summary = MarkdownxField(blank=True, null=True)
+    summary = MarkdownxField(blank=True)
     tags = TagField(force_lowercase=True,
                     get_absolute_url=lambda tag: reverse_lazy('articles:list_tag', kwargs={'tag': tag.slug}))
     created = models.DateTimeField(auto_now_add=True)