diff --git a/moto/iam/models.py b/moto/iam/models.py
index 4b6c340e..4bc7a544 100644
--- a/moto/iam/models.py
+++ b/moto/iam/models.py
@@ -764,13 +764,13 @@ class IAMBackend(BaseBackend):
             role.tags.pop(ref_key, None)
 
     def create_policy_version(self, policy_arn, policy_document, set_as_default):
+        iam_policy_document_validator = IAMPolicyDocumentValidator(policy_document)
+        iam_policy_document_validator.validate()
+
         policy = self.get_policy(policy_arn)
         if not policy:
             raise IAMNotFoundException("Policy not found")
 
-        iam_policy_document_validator = IAMPolicyDocumentValidator(policy_document)
-        iam_policy_document_validator.validate()
-
         version = PolicyVersion(policy_arn, policy_document, set_as_default)
         policy.versions.append(version)
         version.version_id = 'v{0}'.format(policy.next_version_num)