diff --git a/core/api/src/main/java/org/onosproject/core/ApplicationId.java b/core/api/src/main/java/org/onosproject/core/ApplicationId.java
index f7f8dfa..b15c9c8 100644
--- a/core/api/src/main/java/org/onosproject/core/ApplicationId.java
+++ b/core/api/src/main/java/org/onosproject/core/ApplicationId.java
@@ -22,7 +22,7 @@
 public interface ApplicationId {
 
     /**
-     * Returns the application id.
+     * Returns the application id. This must be non-negative.
      * @return a short value
      */
     short id();