diff --git a/akka-stream/src/main/scala/akka/stream/impl/fusing/GraphInterpreter.scala b/akka-stream/src/main/scala/akka/stream/impl/fusing/GraphInterpreter.scala
index e17da07184..70fc0c7c8e 100644
--- a/akka-stream/src/main/scala/akka/stream/impl/fusing/GraphInterpreter.scala
+++ b/akka-stream/src/main/scala/akka/stream/impl/fusing/GraphInterpreter.scala
@@ -668,10 +668,15 @@ import akka.stream.snapshot._
         logicSnapshots(logicIndexes(connection.inOwner)),
         logicSnapshots(logicIndexes(connection.outOwner)),
         connection.portState match {
-          case InReady  => ConnectionSnapshot.ShouldPull
-          case OutReady => ConnectionSnapshot.ShouldPush
-          case x if (x | InClosed | OutClosed) == (InClosed | OutClosed) =>
+          case InReady                                                     => ConnectionSnapshot.ShouldPull
+          case OutReady                                                    => ConnectionSnapshot.ShouldPush
+          case x if (x & (InClosed | OutClosed)) == (InClosed | OutClosed) =>
+            // At least one side of the connection is closed: we show it as closed
             ConnectionSnapshot.Closed
+          case _ =>
+            // This should not be possible: connection alive and both push and pull enqueued but not received
+            throw new IllegalStateException(s"Unexpected connection state for $connection: ${connection.portState}")
+
         })
     }