diff --git a/rest_framework/serializers.py b/rest_framework/serializers.py
index 49eec82591..13e93ef9ff 100644
--- a/rest_framework/serializers.py
+++ b/rest_framework/serializers.py
@@ -209,7 +209,7 @@ def save(self, **kwargs):
 
         return self.instance
 
-    def is_valid(self, raise_exception=False):
+    def is_valid(self, *, raise_exception=False):
         assert hasattr(self, 'initial_data'), (
             'Cannot call `.is_valid()` as no `data=` keyword argument was '
             'passed when instantiating the serializer instance.'
@@ -712,7 +712,7 @@ def save(self, **kwargs):
 
         return self.instance
 
-    def is_valid(self, raise_exception=False):
+    def is_valid(self, *, raise_exception=False):
         # This implementation is the same as the default,
         # except that we use lists, rather than dicts, as the empty case.
         assert hasattr(self, 'initial_data'), (