diff --git a/compatibility_matrices/compatibility_matrix.3.xml b/compatibility_matrices/compatibility_matrix.3.xml
index 468735d..0964c99 100644
--- a/compatibility_matrices/compatibility_matrix.3.xml
+++ b/compatibility_matrices/compatibility_matrix.3.xml
@@ -183,7 +183,10 @@
             <instance>default</instance>
         </interface>
     </hal>
-    <hal format="hidl" optional="false">
+    <!-- Either the AIDL or the HIDL allocator HAL must exist on the device.
+         If the HIDL composer HAL exists, it must be at least version 2.0.
+         See DeviceManifestTest.GrallocHal -->
+    <hal format="hidl" optional="true">
         <name>android.hardware.graphics.allocator</name>
         <version>2.0</version>
         <interface>