diff --git a/zerver/models.py b/zerver/models.py
index 4f357baa1c..89be1387a4 100644
--- a/zerver/models.py
+++ b/zerver/models.py
@@ -34,6 +34,7 @@ from zerver.lib import cache
 from zerver.lib.validator import check_int, check_float, check_string, \
     check_short_string
 from zerver.lib.name_restrictions import is_disposable_domain
+from zerver.lib.types import Validator
 
 from django.utils.encoding import force_text
 
@@ -1870,9 +1871,9 @@ class CustomProfileField(models.Model):
         (FLOAT, u'Float', check_float, float),
         (SHORT_TEXT, u'Short Text', check_short_string, str),
         (LONG_TEXT, u'Long Text', check_string, str),
-    ]  # type: List[Tuple[int, Text, Callable[[str, Any], str], Callable[[Any], Any]]]
+    ]  # type: List[Tuple[int, Text, Validator, Callable[[Any], Any]]]
 
-    FIELD_VALIDATORS = {item[0]: item[2] for item in FIELD_TYPE_DATA}  # type: Dict[int, Callable[[str, Any], str]]
+    FIELD_VALIDATORS = {item[0]: item[2] for item in FIELD_TYPE_DATA}  # type: Dict[int, Validator]
     FIELD_CONVERTERS = {item[0]: item[3] for item in FIELD_TYPE_DATA}  # type: Dict[int, Callable[[Any], Any]]
     FIELD_TYPE_CHOICES = [(item[0], item[1]) for item in FIELD_TYPE_DATA]  # type: List[Tuple[int, Text]]