diff --git a/core/api/src/main/java/org/onosproject/net/DisjointPath.java b/core/api/src/main/java/org/onosproject/net/DisjointPath.java
index 39059f4..39237ea 100644
--- a/core/api/src/main/java/org/onosproject/net/DisjointPath.java
+++ b/core/api/src/main/java/org/onosproject/net/DisjointPath.java
@@ -43,7 +43,7 @@
     /**
      * Gets secondary path.
      *
-     * @return secondary path
+     * @return secondary path, or null if there is no secondary path available.
      */
     Path backup();
 }
diff --git a/core/common/src/main/java/org/onosproject/common/DefaultTopology.java b/core/common/src/main/java/org/onosproject/common/DefaultTopology.java
index 8c4fbc8..72780d3 100644
--- a/core/common/src/main/java/org/onosproject/common/DefaultTopology.java
+++ b/core/common/src/main/java/org/onosproject/common/DefaultTopology.java
@@ -482,6 +482,12 @@
     }
 
     private DisjointPath networkDisjointPath(DisjointPathPair<TopologyVertex, TopologyEdge> path) {
+        if (!path.hasBackup()) {
+            // There was no secondary path available.
+            return new DefaultDisjointPath(CORE_PROVIDER_ID,
+                                           (DefaultPath) networkPath(path.primary()),
+                                           null);
+        }
         return new DefaultDisjointPath(CORE_PROVIDER_ID,
                                        (DefaultPath) networkPath(path.primary()),
                                        (DefaultPath) networkPath(path.secondary()));