diff --git a/readthedocs/api/v3/serializers.py b/readthedocs/api/v3/serializers.py
index 5b3361259ef..8ef11514ecb 100644
--- a/readthedocs/api/v3/serializers.py
+++ b/readthedocs/api/v3/serializers.py
@@ -526,7 +526,7 @@ class SubprojectCreateSerializer(FlexFieldsModelSerializer):
 
     child = serializers.SlugRelatedField(
         slug_field='slug',
-        queryset=Project.objects.all(),
+        queryset=Project.objects.none(),
     )
 
     class Meta:
@@ -545,6 +545,10 @@ def __init__(self, *args, **kwargs):
 
         super().__init__(*args, **kwargs)
 
+        user = self.context['request'].user
+        # TODO: Filter projects using project restrictions for subproject.
+        self.fields['child'].queryset = user.projects.all()
+
     def validate_child(self, value):
         # Check the user is maintainer of the child project
         user = self.context['request'].user