diff --git a/experimental/puppeteer-firefox/lib/helper.js b/experimental/puppeteer-firefox/lib/helper.js
index 30d1b867be5bd..81dd61d6808c8 100644
--- a/experimental/puppeteer-firefox/lib/helper.js
+++ b/experimental/puppeteer-firefox/lib/helper.js
@@ -32,7 +32,7 @@ class Helper {
         return method.call(this, ...args).catch(e => {
           const stack = syncStack.stack.substring(syncStack.stack.indexOf('\n') + 1);
           const clientStack = stack.substring(stack.indexOf('\n'));
-          if (!e.stack.includes(clientStack))
+          if (e instanceof Error && e.stack && !e.stack.includes(clientStack))
             e.stack += '\n  -- ASYNC --\n' + stack;
           throw e;
         });
diff --git a/lib/helper.js b/lib/helper.js
index ee1055c70a4a0..f434707c4fae2 100644
--- a/lib/helper.js
+++ b/lib/helper.js
@@ -109,7 +109,7 @@ class Helper {
         return method.call(this, ...args).catch(e => {
           const stack = syncStack.stack.substring(syncStack.stack.indexOf('\n') + 1);
           const clientStack = stack.substring(stack.indexOf('\n'));
-          if (!e.stack.includes(clientStack))
+          if (e instanceof Error && e.stack && !e.stack.includes(clientStack))
             e.stack += '\n  -- ASYNC --\n' + stack;
           throw e;
         });