diff --git a/schema/Subscription.json b/schema/Subscription.json
index b4762d4bed0626aabaaf19422161a6bfcd4f3f28..d8abaea52bc8c0a75efd4bb2fb59a701adebb5e9 100644
--- a/schema/Subscription.json
+++ b/schema/Subscription.json
@@ -11,8 +11,10 @@
           "type": "array",
           "minItems": 1,
           "items": {
-            "type": "string"
-          }
+            "type": "string",
+            "minLength": 1
+          },
+          "uniqueItems": true
         },
         "format": {
           "type": "string"
@@ -140,7 +142,8 @@
       "type": "array",
       "minItems": 1,
       "items": {
-        "type": "string"
+        "type": "string",
+        "minLength": 1
       },
       "uniqueItems": true
     },
@@ -180,8 +183,26 @@
   "modifiedAt": {
     "$ref": "https://forge.etsi.org/gitlab/NGSI-LD/NGSI-LD/raw/master/schema/common.json#/definitions/modifiedAt"
   },
-  "required": [
-    "id",
-    "type"
+  "allOf": [
+    {
+      "required": [
+        "id",
+        "type"
+      ]
+    },
+    {
+      "anyOf": [
+        {
+          "required": [
+            "entities"
+          ]
+        },
+        {
+          "required": [
+            "watchedAttributes"
+          ]
+        }
+      ]
+    }
   ]
 }
diff --git a/schema/common.json b/schema/common.json
index 05e41dbd9e9b898223ded76156b8760646724e29..9e3415710d3db558b8efd9eff79f637bd4cbb971 100644
--- a/schema/common.json
+++ b/schema/common.json
@@ -76,7 +76,8 @@
           "type": "string",
           "format": "regex"
         }
-      }
+      },
+      "required": ["type"]
     }
   }
 }