diff --git a/compatibility_matrix.27.xml b/compatibility_matrix.27.xml
index 22ca426..5c81f26 100644
--- a/compatibility_matrix.27.xml
+++ b/compatibility_matrix.27.xml
@@ -71,7 +71,7 @@
             <instance>legacy/0</instance>
         </interface>
     </hal>
-    <hal format="hidl" optional="false">
+    <hal format="hidl" optional="true">
         <name>android.hardware.cas</name>
         <version>1.0</version>
         <interface>