diff --git a/akka-docs/src/main/paradox/scala/stream/stages-overview.md b/akka-docs/src/main/paradox/scala/stream/stages-overview.md
index c2aeea459f..b9ad16f7c7 100644
--- a/akka-docs/src/main/paradox/scala/stream/stages-overview.md
+++ b/akka-docs/src/main/paradox/scala/stream/stages-overview.md
@@ -541,6 +541,24 @@ Sources and sinks for integrating with `java.io.InputStream` and `java.io.Output
 `StreamConverters`. As they are blocking APIs the implementations of these stages are run on a separate
 dispatcher configured through the `akka.stream.blocking-io-dispatcher`.
 
+@@@ warning
+
+Be aware that `asInputStream` and `asOutputStream` materialize `InputStream` and `OutputStream` respectively as
+blocking API implementation. They will block tread until data will be available from upstream.
+Because of blocking nature these objects cannot be used in `mapMaterializeValue` section as it causes deadlock
+of the stream materialization process.
+For example, following snippet will fall with timeout exception:
+
+```scala
+...
+.toMat(StreamConverters.asInputStream().mapMaterializedValue { inputStream ⇒
+        inputStream.read()  // this could block forever
+        ...
+}).run()
+```
+
+@@@
+
 ---------------------------------------------------------------
 
 ### fromOutputStream