diff --git a/django/core/management/validation.py b/django/core/management/validation.py
index 1dc7620..08749cc 100644
--- a/django/core/management/validation.py
+++ b/django/core/management/validation.py
@@ -110,6 +110,11 @@ def get_validation_errors(outfile, app=None):
                 # so skip the next section
                 if isinstance(f.rel.to, (str, unicode)):
                     continue
+            
+            # Check that the field is not set to unique.  ManyToManyFields do not support unique.
+            if f.unique:
+                e.add(opts, "ManyToManyFields cannot be unique.  Remove the unique argument on '%s'." % f.name)
+            
             if getattr(f.rel, 'through', None) is not None:
                 if hasattr(f.rel, 'through_model'):
                     from_model, to_model = cls, f.rel.to
diff --git a/tests/modeltests/invalid_models/models.py b/tests/modeltests/invalid_models/models.py
index c450193..7d83274 100644
--- a/tests/modeltests/invalid_models/models.py
+++ b/tests/modeltests/invalid_models/models.py
@@ -177,6 +177,10 @@ class AbstractRelationModel(models.Model):
     fk1 = models.ForeignKey('AbstractModel')
     fk2 = models.ManyToManyField('AbstractModel')
     
+class UniqueM2M(models.Model):
+    """ Model to test for unique ManyToManyFields, which are invalid. """
+    unique_people = models.ManyToManyField( Person, unique=True )
+    
 model_errors = """invalid_models.fielderrors: "charfield": CharFields require a "max_length" attribute.
 invalid_models.fielderrors: "decimalfield": DecimalFields require a "decimal_places" attribute.
 invalid_models.fielderrors: "decimalfield": DecimalFields require a "max_digits" attribute.
@@ -271,4 +275,5 @@ invalid_models.personselfrefm2m: Intermediary model RelationshipTripleFK has mor
 invalid_models.personselfrefm2mexplicit: Many-to-many fields with intermediate tables cannot be symmetrical.
 invalid_models.abstractrelationmodel: 'fk1' has a relation with model AbstractModel, which has either not been installed or is abstract.
 invalid_models.abstractrelationmodel: 'fk2' has an m2m relation with model AbstractModel, which has either not been installed or is abstract.
+invalid_models.uniquem2m: ManyToManyFields cannot be unique.  Remove the unique argument on 'unique_people'.
 """