1 files changed, 11 insertions, 1 deletions
diff --git a/lib/internal/queue.js b/lib/internal/queue.js
index c73c322..44f1c01 100644
--- a/lib/internal/queue.js
+++ b/lib/internal/queue.js
@@ -70,11 +70,14 @@ export default function queue(worker, concurrency, payload) {
             if (q.idle()) {
                 q.drain();
             }
-            q.process();
+            if (!sync) {
+                q.process();
+            }
         });
     }
 
     var workers = 0;
+    var sync = 0;
     var workersList = [];
     var q = {
         _tasks: new DLL(),
@@ -120,7 +123,14 @@ export default function queue(worker, concurrency, payload) {
                 }
 
                 var cb = onlyOnce(_next(tasks));
+
+                // prevent stack growth when calling callback synchronously:
+                // unroll the recursion into a loop here. (The callback will
+                // have reduced the workers count synchronously, causing us to
+                // loop again)
+                sync = 1;
                 worker(data, cb);
+                sync = 0;
             }
         },
         length: function () {