diff --git a/client/src/client/workers/test-evaluator.js b/client/src/client/workers/test-evaluator.js
index df0b6ea1a8..30584bd40e 100644
--- a/client/src/client/workers/test-evaluator.js
+++ b/client/src/client/workers/test-evaluator.js
@@ -18,7 +18,7 @@ const __utils = (() => {
 
   const oldLog = self.console.log.bind(self.console);
   self.console.log = function proxyConsole(...args) {
-    logs.push(args.map(arg => JSON.stringify(arg)).join(' '));
+    logs.push(args.map(arg => '' + JSON.stringify(arg)).join(' '));
     if (logs.join('\n').length > MAX_LOGS_SIZE) {
       flushLogs();
     }
diff --git a/client/src/templates/Challenges/utils/frame.js b/client/src/templates/Challenges/utils/frame.js
index c022071657..da021b4f82 100644
--- a/client/src/templates/Challenges/utils/frame.js
+++ b/client/src/templates/Challenges/utils/frame.js
@@ -83,7 +83,7 @@ const mountFrame = document => ({ element, ...rest }) => {
 const buildProxyConsole = proxyLogger => ctx => {
   const oldLog = ctx.window.console.log.bind(ctx.window.console);
   ctx.window.console.log = function proxyConsole(...args) {
-    proxyLogger(args.map(arg => JSON.stringify(arg)).join(' '));
+    proxyLogger(args.map(arg => '' + JSON.stringify(arg)).join(' '));
     return oldLog(...args);
   };
   return ctx;