diff --git a/akka-stream-tests/src/test/scala/akka/stream/scaladsl/FlowGroupBySpec.scala b/akka-stream-tests/src/test/scala/akka/stream/scaladsl/FlowGroupBySpec.scala
index 36315344f6..ae0fde4516 100644
--- a/akka-stream-tests/src/test/scala/akka/stream/scaladsl/FlowGroupBySpec.scala
+++ b/akka-stream-tests/src/test/scala/akka/stream/scaladsl/FlowGroupBySpec.scala
@@ -149,7 +149,7 @@ class FlowGroupBySpec extends StreamSpec {
     }
 
     "accept cancellation of substreams" in assertAllStagesStopped {
-      new SubstreamsSupport(groupCount = 2) {
+      new SubstreamsSupport(groupCount = 2, maxSubstreams = 3) {
         StreamPuppet(getSubFlow(1).runWith(Sink.asPublisher(false))).cancel()
 
         val substream = StreamPuppet(getSubFlow(0).runWith(Sink.asPublisher(false)))
diff --git a/akka-stream/src/main/scala/akka/stream/impl/fusing/StreamOfStreams.scala b/akka-stream/src/main/scala/akka/stream/impl/fusing/StreamOfStreams.scala
index 7489d0d7a4..e4e412318d 100644
--- a/akka-stream/src/main/scala/akka/stream/impl/fusing/StreamOfStreams.scala
+++ b/akka-stream/src/main/scala/akka/stream/impl/fusing/StreamOfStreams.scala
@@ -334,7 +334,7 @@ import akka.stream.impl.fusing.GraphStages.SingleSource
           nextElementValue = elem
         }
       } else {
-        if (activeSubstreamsMap.size == maxSubstreams)
+        if (activeSubstreamsMap.size + closedSubstreams.size == maxSubstreams)
           throw tooManySubstreamsOpenException
         else if (closedSubstreams.contains(key) && !hasBeenPulled(in))
           pull(in)