diff --git a/moto/ecr/policy_validation.py b/moto/ecr/policy_validation.py
index 286599d..83a68e7 100644
--- a/moto/ecr/policy_validation.py
+++ b/moto/ecr/policy_validation.py
@@ -15,6 +15,7 @@
 VALID_SELECTION_PROPERTIES = {
     "tagPrefixList",
     "countUnit",
+    "maximumSemanticsRetainCount",
     *REQUIRED_SELECTION_PROPERTIES,
 }