diff --git a/source/java/org/alfresco/repo/rating/RatingServiceImpl.java b/source/java/org/alfresco/repo/rating/RatingServiceImpl.java
index 80f89c2174..6d856dbc09 100644
--- a/source/java/org/alfresco/repo/rating/RatingServiceImpl.java
+++ b/source/java/org/alfresco/repo/rating/RatingServiceImpl.java
@@ -328,7 +328,14 @@ public class RatingServiceImpl implements RatingService
                 }
             }
         }
-        return (float)ratingTotal / (float)ratingCount;
+        if (ratingCount == 0)
+        {
+            return -1;
+        }
+        else
+        {
+            return (float)ratingTotal / (float)ratingCount;
+        }
     }
 
     public int getRatingsCount(NodeRef targetNode, String ratingSchemeName)
diff --git a/source/java/org/alfresco/service/cmr/rating/RatingService.java b/source/java/org/alfresco/service/cmr/rating/RatingService.java
index 356361ac93..47432cd700 100644
--- a/source/java/org/alfresco/service/cmr/rating/RatingService.java
+++ b/source/java/org/alfresco/service/cmr/rating/RatingService.java
@@ -95,6 +95,13 @@ public interface RatingService
 
     int getTotalRating(NodeRef targetNode, String ratingSchemeName);
 
+    /**
+     * This method returns the average (mean) rating in the specified scheme for the
+     * specified nodeRef. If there have been no ratings applied, -1 is returned.
+     * @param targetNode the node for which an average is sought.
+     * @param ratingSchemeName the rating scheme name in which the average is defined.
+     * @return the average (mean) value if there is one, else -1.
+     */
     float getAverageRating(NodeRef targetNode, String ratingSchemeName);
 
     /**