diff --git a/js/src/redux/providers/certifications/middleware.js b/js/src/redux/providers/certifications/middleware.js
index a1403ee3a..b70ff4909 100644
--- a/js/src/redux/providers/certifications/middleware.js
+++ b/js/src/redux/providers/certifications/middleware.js
@@ -128,7 +128,8 @@ export default class CertificationsMiddleware {
         return badgeReg.getContract()
           .then((badgeRegContract) => {
             logs = badgeRegContract.parseEventLogs(logs);
-            const ids = logs.map((log) => log.params.id.value.toNumber());
+
+            const ids = logs.map((log) => log.params && log.params.id.value.toNumber());
 
             return fetchCertifiers(uniq(ids));
           });
diff --git a/js/src/views/Contract/contract.js b/js/src/views/Contract/contract.js
index 4af775cef..cc6b35d2b 100644
--- a/js/src/views/Contract/contract.js
+++ b/js/src/views/Contract/contract.js
@@ -101,8 +101,14 @@ class Contract extends Component {
     const { api } = this.context;
     const { subscriptionId, blockSubscriptionId, contract } = this.state;
 
-    api.unsubscribe(blockSubscriptionId);
-    contract.unsubscribe(subscriptionId);
+    if (blockSubscriptionId >= 0) {
+      api.unsubscribe(blockSubscriptionId);
+    }
+
+    if (subscriptionId >= 0) {
+      contract.unsubscribe(subscriptionId);
+    }
+
     this.props.setVisibleAccounts([]);
   }