diff --git a/django/db/backends/oracle/base.py b/django/db/backends/oracle/base.py
index b13bab1798..ae77de57d0 100644
--- a/django/db/backends/oracle/base.py
+++ b/django/db/backends/oracle/base.py
@@ -111,7 +111,7 @@ class DatabaseWrapper(BaseDatabaseWrapper):
     }
     data_type_check_constraints = {
         'BooleanField': '%(qn_column)s IN (0,1)',
-        'NullBooleanField': '(%(qn_column)s IN (0,1)) OR (%(qn_column)s IS NULL)',
+        'NullBooleanField': '%(qn_column)s IN (0,1)',
         'PositiveIntegerField': '%(qn_column)s >= 0',
         'PositiveSmallIntegerField': '%(qn_column)s >= 0',
     }