diff --git a/django/core/management/validation.py b/django/core/management/validation.py
index 1dc76205c8d..0b3542c66d0 100644
--- a/django/core/management/validation.py
+++ b/django/core/management/validation.py
@@ -99,7 +99,7 @@ def get_validation_errors(outfile, app=None):
                         if r.get_accessor_name() == rel_query_name:
                             e.add(opts, "Reverse query name for field '%s' clashes with related field '%s.%s'. Add a related_name argument to the definition for '%s'." % (f.name, rel_opts.object_name, r.get_accessor_name(), f.name))
 
-        seen_intermediary_signatures = [] 
+        seen_intermediary_signatures = []
         for i, f in enumerate(opts.local_many_to_many):
             # Check to see if the related m2m field will clash with any
             # existing fields, m2m fields, m2m related objects or related
@@ -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
@@ -152,7 +157,7 @@ def get_validation_errors(outfile, app=None):
                         e.add(opts, "'%s' has a manually-defined m2m relation through model %s, which does not have foreign keys to %s and %s" % (f.name, f.rel.through, f.rel.to._meta.object_name, cls._meta.object_name))
                 else:
                     e.add(opts, "'%s' specifies an m2m relation through model %s, which has not been installed" % (f.name, f.rel.through))
-            
+
             rel_opts = f.rel.to._meta
             rel_name = RelatedObject(f.rel.to, cls, f).get_accessor_name()
             rel_query_name = f.related_query_name()
diff --git a/tests/modeltests/invalid_models/models.py b/tests/modeltests/invalid_models/models.py
index c450193d975..abd72b12938 100644
--- a/tests/modeltests/invalid_models/models.py
+++ b/tests/modeltests/invalid_models/models.py
@@ -110,11 +110,11 @@ class Car(models.Model):
 class MissingRelations(models.Model):
     rel1 = models.ForeignKey("Rel1")
     rel2 = models.ManyToManyField("Rel2")
-    
+
 class MissingManualM2MModel(models.Model):
     name = models.CharField(max_length=5)
     missing_m2m = models.ManyToManyField(Model, through="MissingM2MModel")
-    
+
 class Person(models.Model):
     name = models.CharField(max_length=5)
 
@@ -176,7 +176,11 @@ class AbstractModel(models.Model):
 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'.
 """