diff --git a/src/Kestrel.Core/Internal/Http2/Http2Connection.cs b/src/Kestrel.Core/Internal/Http2/Http2Connection.cs
index ae2b7d5bed..87adced245 100644
--- a/src/Kestrel.Core/Internal/Http2/Http2Connection.cs
+++ b/src/Kestrel.Core/Internal/Http2/Http2Connection.cs
@@ -218,9 +218,9 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http2
                     return ProcessWindowUpdateFrameAsync();
                 case Http2FrameType.CONTINUATION:
                     return ProcessContinuationFrameAsync<TContext>(application);
+                default:
+                    return ProcessUnknownFrameAsync();
             }
-
-            return Task.CompletedTask;
         }
 
         private Task ProcessDataFrameAsync()
@@ -454,6 +454,16 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http2
             return Task.CompletedTask;
         }
 
+        private Task ProcessUnknownFrameAsync()
+        {
+            if (_currentHeadersStream != null)
+            {
+                throw new Http2ConnectionErrorException(Http2ErrorCode.PROTOCOL_ERROR);
+            }
+
+            return Task.CompletedTask;
+        }
+
         void IHttp2StreamLifetimeHandler.OnStreamCompleted(int streamId)
         {
             _streams.TryRemove(streamId, out _);
diff --git a/test/Kestrel.Core.Tests/Http2ConnectionTests.cs b/test/Kestrel.Core.Tests/Http2ConnectionTests.cs
index 56bd6f3b31..df4621a8b2 100644
--- a/test/Kestrel.Core.Tests/Http2ConnectionTests.cs
+++ b/test/Kestrel.Core.Tests/Http2ConnectionTests.cs
@@ -1062,6 +1062,34 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Core.Tests
             Assert.Equal(_largeHeaderB, responseHeadersDictionary["b"]);
         }
 
+        [Fact]
+        public async Task UnknownFrameType_Received_Ignored()
+        {
+            await InitializeConnectionAsync(_noopApplication);
+
+            await SendUnknownFrameTypeAsync(streamId: 1);
+
+            // Check that the connection is still alive
+            await SendPingAsync();
+            await ExpectAsync(Http2FrameType.PING,
+                withLength: 8,
+                withFlags: (byte)Http2PingFrameFlags.ACK,
+                withStreamId: 0);
+
+            await StopConnectionAsync(0, ignoreNonGoAwayFrames: false);
+        }
+
+        [Fact]
+        public async Task UnknownFrameType_Received_InterleavedWithHeaders_ConnectionError()
+        {
+            await InitializeConnectionAsync(_noopApplication);
+
+            await SendHeadersAsync(1, Http2HeadersFrameFlags.NONE, _browserRequestHeaders);
+            await SendUnknownFrameTypeAsync(streamId: 1);
+
+            await WaitForConnectionErrorAsync(expectedLastStreamId: 0, expectedErrorCode: Http2ErrorCode.PROTOCOL_ERROR, ignoreNonGoAwayFrames: false);
+        }
+
         [Fact]
         public async Task ConnectionError_AbortsAllStreams()
         {
@@ -1451,6 +1479,15 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Core.Tests
             return SendAsync(frame.Raw);
         }
 
+        private Task SendUnknownFrameTypeAsync(int streamId)
+        {
+            var frame = new Http2Frame();
+            frame.StreamId = streamId;
+            frame.Type = (Http2FrameType)42;
+            frame.Length = 0;
+            return SendAsync(frame.Raw);
+        }
+
         private async Task<Http2Frame> ReceiveFrameAsync()
         {
             var frame = new Http2Frame();