diff --git a/map.go b/map.go
index 665af6c..b993582 100644
--- a/map.go
+++ b/map.go
@@ -1,5 +1,7 @@
 package channel
 
+import "sync"
+
 // MapPreserveOrder applies mapper to all I's coming from source and sends their return values to out while preserving input order.
 // All mappings will be done as concurrently as possible using as many threads as there are CPU cores
 func MapPreserveOrder[I, O any](source <-chan I, mapper func(I) O) (out <-chan O) {
@@ -51,12 +53,18 @@ func MapWithRunner[I, O any](source <-chan I, runner Runner, mapper func(I) O) <
 
 	go func() {
 		defer close(out)
+		wg := &sync.WaitGroup{}
+
 		for value := range source {
 			value := value
+			wg.Add(1)
 			runner.Run(func() {
+				defer wg.Done()
 				out <- mapper(value)
 			})
 		}
+
+		wg.Wait()
 	}()
 
 	return out