diff --git a/src/core/Akka.API.Tests/CoreAPISpec.ApproveStreams.approved.txt b/src/core/Akka.API.Tests/CoreAPISpec.ApproveStreams.approved.txt
index 36c9e3c4436..a179c633103 100644
--- a/src/core/Akka.API.Tests/CoreAPISpec.ApproveStreams.approved.txt
+++ b/src/core/Akka.API.Tests/CoreAPISpec.ApproveStreams.approved.txt
@@ -1033,7 +1033,7 @@ namespace Akka.Streams.Dsl
         public Akka.Streams.IGraph<Akka.Streams.BidiShape<TIn1, TOut1, TIn2, TOut2>, TMat> AddAttributes(Akka.Streams.Attributes attributes) { }
         public Akka.Streams.IGraph<Akka.Streams.BidiShape<TIn1, TOut1, TIn2, TOut2>, TMat> Async() { }
         public Akka.Streams.Dsl.BidiFlow<TIn1, TOut12, TIn21, TOut2, TMat> Atop<TOut12, TIn21, TMat2>(Akka.Streams.Dsl.BidiFlow<TOut1, TOut12, TIn21, TIn2, TMat2> bidi) { }
-        public Akka.Streams.Dsl.BidiFlow<TIn1, TOut12, TIn21, TOut2, TMat> AtopMat<TOut12, TIn21, TMat2, TMat3>(Akka.Streams.Dsl.BidiFlow<TOut1, TOut12, TIn21, TIn2, TMat2> bidi, System.Func<TMat, TMat2, TMat3> combine) { }
+        public Akka.Streams.Dsl.BidiFlow<TIn1, TOut12, TIn21, TOut2, TMat3> AtopMat<TOut12, TIn21, TMat2, TMat3>(Akka.Streams.Dsl.BidiFlow<TOut1, TOut12, TIn21, TIn2, TMat2> bidi, System.Func<TMat, TMat2, TMat3> combine) { }
         public Akka.Streams.Dsl.Flow<TIn1, TOut2, TMat> Join<TMat2>(Akka.Streams.Dsl.Flow<TOut1, TIn2, TMat2> flow) { }
         public Akka.Streams.Dsl.Flow<TIn1, TOut2, TMat3> JoinMat<TMat2, TMat3>(Akka.Streams.Dsl.Flow<TOut1, TIn2, TMat2> flow, System.Func<TMat, TMat2, TMat3> combine) { }
         public Akka.Streams.IGraph<Akka.Streams.BidiShape<TIn1, TOut1, TIn2, TOut2>, TMat> Named(string name) { }
diff --git a/src/core/Akka.Streams/Dsl/BidiFlow.cs b/src/core/Akka.Streams/Dsl/BidiFlow.cs
index 46b52ed4ad6..6b4d094e0bb 100644
--- a/src/core/Akka.Streams/Dsl/BidiFlow.cs
+++ b/src/core/Akka.Streams/Dsl/BidiFlow.cs
@@ -278,13 +278,13 @@ public BidiFlow<TIn1, TOut12, TIn21, TOut2, TMat> Atop<TOut12, TIn21, TMat2>(Bid
         /// <param name="bidi">TBD</param>
         /// <param name="combine">TBD</param>
         /// <returns>TBD</returns>
-        public BidiFlow<TIn1, TOut12, TIn21, TOut2, TMat> AtopMat<TOut12, TIn21, TMat2, TMat3>(BidiFlow<TOut1, TOut12, TIn21, TIn2, TMat2> bidi, Func<TMat, TMat2, TMat3> combine)
+        public BidiFlow<TIn1, TOut12, TIn21, TOut2, TMat3> AtopMat<TOut12, TIn21, TMat2, TMat3>(BidiFlow<TOut1, TOut12, TIn21, TIn2, TMat2> bidi, Func<TMat, TMat2, TMat3> combine)
         {
             var copy = bidi.Module.CarbonCopy();
             var ins = copy.Shape.Inlets.ToArray();
             var outs = copy.Shape.Outlets.ToArray();
 
-            return new BidiFlow<TIn1, TOut12, TIn21, TOut2, TMat>(Module
+            return new BidiFlow<TIn1, TOut12, TIn21, TOut2, TMat3>(Module
                 .Compose(copy, combine)
                 .Wire(Shape.Outlet1, ins[0])
                 .Wire(outs[1], Shape.Inlet2)