diff --git a/readthedocs/projects/forms.py b/readthedocs/projects/forms.py
index a2f868c8a3c..caaeef9d0de 100644
--- a/readthedocs/projects/forms.py
+++ b/readthedocs/projects/forms.py
@@ -270,6 +270,13 @@ def clean_parent(self):
                 _('Subproject nesting is not supported'))
         return self.project
 
+    def clean_child(self):
+        child = self.cleaned_data['child']
+        if child == self.project:
+            raise forms.ValidationError(
+                _('A project can not be a subproject of itself'))
+        return child
+
     def get_subproject_queryset(self):
         """
         Return scrubbed subproject choice queryset.
@@ -280,7 +287,8 @@ def get_subproject_queryset(self):
         queryset = (
             Project.objects.for_admin_user(self.user)
             .exclude(subprojects__isnull=False)
-            .exclude(superprojects__isnull=False))
+            .exclude(superprojects__isnull=False)
+            .exclude(pk=self.project.pk))
         return queryset
 
 
diff --git a/readthedocs/rtd_tests/tests/test_subprojects.py b/readthedocs/rtd_tests/tests/test_subprojects.py
index d64d3ee3d6b..1d3ac59aeb3 100644
--- a/readthedocs/rtd_tests/tests/test_subprojects.py
+++ b/readthedocs/rtd_tests/tests/test_subprojects.py
@@ -143,6 +143,21 @@ def test_excludes_existing_subprojects(self):
             [''],
         )
 
+    def test_exclude_self_project_as_subproject(self):
+        user = fixture.get(User)
+        project = fixture.get(Project, users=[user])
+
+        form = ProjectRelationshipForm(
+            {'child': project.pk},
+            project=project,
+            user=user
+        )
+        self.assertFalse(form.is_valid())
+        self.assertNotIn(
+            project.id,
+            [proj_id for (proj_id, __) in form.fields['child'].choices]
+        )
+
 
 @override_settings(PUBLIC_DOMAIN='readthedocs.org')
 class ResolverBase(TestCase):