diff --git a/awx/api/fields.py b/awx/api/fields.py
index adc83a8908..3197e80c55 100644
--- a/awx/api/fields.py
+++ b/awx/api/fields.py
@@ -101,6 +101,10 @@ class DeprecatedCredentialField(serializers.IntegerField):
         super(DeprecatedCredentialField, self).__init__(**kwargs)
 
     def to_internal_value(self, pk):
+        try:
+            pk = int(pk)
+        except ValueError:
+            self.fail('invalid')
         try:
             Credential.objects.get(pk=pk)
         except ObjectDoesNotExist: