diff --git a/lib/http/2/connection.rb b/lib/http/2/connection.rb
index d3cf180..40a7c13 100644
--- a/lib/http/2/connection.rb
+++ b/lib/http/2/connection.rb
@@ -129,7 +129,6 @@ def new_stream(**args)
       connection_error(:protocol_error, msg: "id is smaller than previous") if @stream_id < @last_stream_id
 
       stream = activate_stream(id: @stream_id, **args)
-      @last_stream_id = stream.id
 
       @stream_id += 2
 
@@ -766,6 +765,7 @@ def activate_stream(id:, **args)
       raise StreamLimitExceeded if @active_stream_count >= @local_settings[:settings_max_concurrent_streams]
 
       stream = Stream.new(connection: self, id: id, **args)
+      @last_stream_id = id
 
       stream.once(:close) do
         @streams.delete(id)
@@ -799,7 +799,6 @@ def verify_stream_order(id)
       return unless id.odd?
 
       connection_error(msg: "Stream ID smaller than previous") if @last_stream_id >= id
-      @last_stream_id = id
     end
 
     def _verify_pseudo_headers(frame, mandatory_headers)
diff --git a/lib/http/2/flow_buffer.rb b/lib/http/2/flow_buffer.rb
index ecf19eb..56fb2e1 100644
--- a/lib/http/2/flow_buffer.rb
+++ b/lib/http/2/flow_buffer.rb
@@ -122,6 +122,11 @@ def initialize
       @bytesize = 0
     end
 
+    def clear
+      @buffer.clear
+      @bytesize = 0
+    end
+
     def <<(frame)
       @buffer << frame
       @bytesize += frame[:payload].bytesize
diff --git a/sig/frame_buffer.rbs b/sig/frame_buffer.rbs
index 8dbaaed..57cb53f 100644
--- a/sig/frame_buffer.rbs
+++ b/sig/frame_buffer.rbs
@@ -4,6 +4,8 @@ module HTTP2
 
     @buffer: Array[data_frame]
 
+    def clear: () -> void
+
     def <<: (data_frame frame) -> void
 
     def empty?: () -> bool