diff --git a/rest_framework/serializers.py b/rest_framework/serializers.py
index e1513440c..c20b60aad 100644
--- a/rest_framework/serializers.py
+++ b/rest_framework/serializers.py
@@ -894,6 +894,10 @@ class ModelSerializer(Serializer):
         models.GenericIPAddressField: IPAddressField,
         models.FilePathField: FilePathField,
     }
+    if postgres_fields:
+        serializer_field_mapping[postgres_fields.HStoreField] = HStoreField
+        serializer_field_mapping[postgres_fields.ArrayField] = ListField
+        serializer_field_mapping[postgres_fields.JSONField] = JSONField
     serializer_related_field = PrimaryKeyRelatedField
     serializer_related_to_field = SlugRelatedField
     serializer_url_field = HyperlinkedIdentityField
@@ -1584,12 +1588,6 @@ class ModelSerializer(Serializer):
         return validators
 
 
-if postgres_fields:
-    ModelSerializer.serializer_field_mapping[postgres_fields.HStoreField] = HStoreField
-    ModelSerializer.serializer_field_mapping[postgres_fields.ArrayField] = ListField
-    ModelSerializer.serializer_field_mapping[postgres_fields.JSONField] = JSONField
-
-
 class HyperlinkedModelSerializer(ModelSerializer):
     """
     A type of `ModelSerializer` that uses hyperlinked relationships instead