diff --git a/django/contrib/admin/validation.py b/django/contrib/admin/validation.py
index 47b70a72db..726da650a6 100644
--- a/django/contrib/admin/validation.py
+++ b/django/contrib/admin/validation.py
@@ -219,19 +219,24 @@ def validate_base(cls, model):
                 raise ImproperlyConfigured("'fields' key is required in "
                         "%s.fieldsets[%d][1] field options dict."
                         % (cls.__name__, idx))
-            for field in fieldset[1]['fields']:
-                check_formfield(cls, model, opts, "fieldsets[%d][1]['fields']" % idx, field)
-                try:
-                    f = opts.get_field(field)
-                    if isinstance(f, models.ManyToManyField) and not f.rel.through._meta.auto_created:
-                        raise ImproperlyConfigured("'%s.fieldsets[%d][1]['fields']' "
-                            "can't include the ManyToManyField field '%s' because "
-                            "'%s' manually specifies a 'through' model." % (
-                                cls.__name__, idx, field, field))
-                except models.FieldDoesNotExist:
-                    # If we can't find a field on the model that matches,
-                    # it could be an extra field on the form.
-                    pass
+            for fields in fieldset[1]['fields']:
+                # The entry in fields might be a tuple. If it is a standalone
+                # field, make it into a tuple to make processing easier.
+                if type(fields) != tuple:
+                    fields = (fields,)
+                for field in fields:
+                    check_formfield(cls, model, opts, "fieldsets[%d][1]['fields']" % idx, field)
+                    try:
+                        f = opts.get_field(field)
+                        if isinstance(f, models.ManyToManyField) and not f.rel.through._meta.auto_created:
+                            raise ImproperlyConfigured("'%s.fieldsets[%d][1]['fields']' "
+                                "can't include the ManyToManyField field '%s' because "
+                                "'%s' manually specifies a 'through' model." % (
+                                    cls.__name__, idx, field, field))
+                    except models.FieldDoesNotExist:
+                        # If we can't find a field on the model that matches,
+                        # it could be an extra field on the form.
+                        pass
         flattened_fieldsets = flatten_fieldsets(cls.fieldsets)
         if len(flattened_fieldsets) > len(set(flattened_fieldsets)):
             raise ImproperlyConfigured('There are duplicate field(s) in %s.fieldsets' % cls.__name__)
diff --git a/tests/regressiontests/admin_validation/models.py b/tests/regressiontests/admin_validation/models.py
index 1a34e4d30c..eb53a9dd6e 100644
--- a/tests/regressiontests/admin_validation/models.py
+++ b/tests/regressiontests/admin_validation/models.py
@@ -32,6 +32,8 @@ class Author(models.Model):
 
 class Book(models.Model):
     name = models.CharField(max_length=100)
+    subtitle = models.CharField(max_length=100)
+    price = models.FloatField()
     authors = models.ManyToManyField(Author, through='AuthorsBooks')
 
 
@@ -131,6 +133,13 @@ Traceback (most recent call last):
    ...
 ImproperlyConfigured: 'FieldsetBookAdmin.fieldsets[1][1]['fields']' can't include the ManyToManyField field 'authors' because 'authors' manually specifies a 'through' model.
 
+>>> class NestedFieldsetAdmin(admin.ModelAdmin):
+...    fieldsets = (
+...        ('Main', {'fields': ('price', ('name', 'subtitle'))}),
+...    )
+
+>>> validate(NestedFieldsetAdmin, Book)
+
 # Regression test for #12209 -- If the explicitly provided through model
 # is specified as a string, the admin should still be able use
 # Model.m2m_field.through