diff --git a/stream/stream.go b/stream/stream.go
index 6b11e90..704d540 100644
--- a/stream/stream.go
+++ b/stream/stream.go
@@ -2,6 +2,7 @@
 package stream
 
 import (
+	"runtime"
 	"sync"
 
 	"github.com/sourcegraph/conc"
@@ -109,7 +110,14 @@ func (s *Stream) WithMaxGoroutines(n int) *Stream {
 
 func (s *Stream) init() {
 	s.initOnce.Do(func() {
-		s.queue = make(chan callbackCh, s.pool.MaxGoroutines()+1)
+		maxGoroutines := s.pool.MaxGoroutines()
+		if maxGoroutines == 0 {
+			// When no goroutine limit is set, use a buffer based on
+			// GOMAXPROCS so that task submission does not block on the
+			// queue, avoiding accidentally serialized execution.
+			maxGoroutines = runtime.GOMAXPROCS(0)
+		}
+		s.queue = make(chan callbackCh, maxGoroutines+1)
 
 		// Start the callbacker.
 		s.callbackerHandle.Go(s.callbacker)