1 files changed, 4 insertions, 3 deletions
diff --git a/lib/child_process.js b/lib/child_process.js
index 972f68ce27..ecd7559abb 100644
--- a/lib/child_process.js
+++ b/lib/child_process.js
@@ -709,9 +709,10 @@ ChildProcess.prototype.spawn = function(options) {
   }
 
   // At least 3 stdio will be created
-  if (stdio.length < 3) {
-    stdio = stdio.concat(new Array(3 - stdio.length));
-  }
+  // Don't concat() a new Array() because it would be sparse, and
+  // stdio.reduce() would skip the sparse elements of stdio.
+  // See http://stackoverflow.com/a/5501711/3561
+  while (stdio.length < 3) stdio.push(undefined);
 
   // Translate stdio into C++-readable form
   // (i.e. PipeWraps or fds)