diff --git a/test/integration/branches_revert2.js b/test/integration/branches_revert2.js
index 9800c3ad7e1415fd1df5dd1584cbeec4bfb8df98..511b55c41579fd5240066e585b40877354e39c26 100644
--- a/test/integration/branches_revert2.js
+++ b/test/integration/branches_revert2.js
@@ -23,6 +23,7 @@ const MEMORY_MODE = true;
 const commonConf = {
   ipv4: '127.0.0.1',
   currency: 'bb',
+  nbCores:1,
   httpLogs: true,
   forksize: 3,
   sigQty: 1
diff --git a/test/integration/register-fork-blocks.js b/test/integration/register-fork-blocks.js
index cf1faf59ba15289bd67d3cdb067a3cf53b1bd990..09c02dfff7c3e2f8afb3decc5549c7418dc3f7b5 100644
--- a/test/integration/register-fork-blocks.js
+++ b/test/integration/register-fork-blocks.js
@@ -20,6 +20,7 @@ describe("Fork blocks", function() {
     s1 = toolbox.server({
 
       // The common conf
+      nbCores:1,
       medianTimeBlocks: 1,
       avgGenTime: 11,
       udTime0: now,
@@ -35,6 +36,7 @@ describe("Fork blocks", function() {
     s2 = toolbox.server({
 
       // Particular conf
+      nbCores:1,
       switchOnHeadAdvance: 5,
       forksize,
 
@@ -47,6 +49,7 @@ describe("Fork blocks", function() {
     s3 = toolbox.server({
 
       // Particular conf
+      nbCores:1,
       switchOnHeadAdvance: 5,
       forksize,