diff --git a/models/yang/mano-types.yang b/models/yang/mano-types.yang
index 7f50c1a..ba917c0 100644
--- a/models/yang/mano-types.yang
+++ b/models/yang/mano-types.yang
@@ -1141,7 +1141,7 @@
         leaf member-vnf-index-ref {
           description
               "Reference to member-vnf within constituent-vnfds";
-          type uint64;
+          type string;
         }
 
         leaf vnfd-id-ref {
diff --git a/models/yang/nsr.yang b/models/yang/nsr.yang
index 4f2eb73..3547866 100644
--- a/models/yang/nsr.yang
+++ b/models/yang/nsr.yang
@@ -486,7 +486,7 @@
           }
 
           leaf member-vnf-index-ref {
-            type uint64;
+            type string;
           }
           leaf vnfd-id-ref {
             description
@@ -912,7 +912,7 @@
               leaf member-vnf-index-ref {
                 description
                    "Reference to member-vnf within constituent-vnfds";
-                type uint64;
+                type string;
               }
 
               leaf vnfd-id-ref {
@@ -1212,7 +1212,7 @@
         leaf member-vnf-index-ref {
           description
               "Reference to member-vnf within constituent-vnfds";
-          type uint64;
+          type string;
         }
 
         leaf vnfd-id-ref {
diff --git a/models/yang/project-nsd.yang b/models/yang/project-nsd.yang
index ae79d96..ace4102 100644
--- a/models/yang/project-nsd.yang
+++ b/models/yang/project-nsd.yang
@@ -63,7 +63,7 @@
           "Identifier/index for the VNFD. This separate id
            is required to ensure that multiple VNFs can be
            part of single NS";
-        type uint64;
+        type string;
       }
 
       leaf vnfd-id-ref {
@@ -97,7 +97,7 @@
           "Identifier/index for the VNFD. This separate id
            is required to ensure that multiple VNFs can be
            part of single NS";
-        type uint64;
+        type string;
       }
 
       leaf vnfd-id-ref {