diff --git a/src/compatibility/android-cdd.html b/src/compatibility/android-cdd.html
index 38c6366..f2a57c5 100644
--- a/src/compatibility/android-cdd.html
+++ b/src/compatibility/android-cdd.html
@@ -710,7 +710,8 @@
  </tr>
  <tr>
     <td>SERIAL</td>
-    <td>A hardware serial number, which MUST be available. The value of this field MUST
+    <td>A hardware serial number, which MUST be available and unique across
+devices with the same MODEL and MANUFACTURER. The value of this field MUST
 be encodable as 7-bit ASCII and match the regular expression &ldquo;^([a-zA-Z0-9]{6,20})$&rdquo;.</td>
  </tr>
  <tr>