diff --git a/lib/websocket/extensions.rb b/lib/websocket/extensions.rb
index 14ca7ab..3ea367a 100644
--- a/lib/websocket/extensions.rb
+++ b/lib/websocket/extensions.rb
@@ -115,6 +115,12 @@ def generate_response(header)
 
       @sessions = sessions
       response.size > 0 ? response.join(', ') : nil
+    ensure
+      if sessions and !sessions.equal?(@sessions)
+        sessions.each do |ext, session|
+          session.close rescue nil
+        end
+      end
     end
 
     def valid_frame_rsv(frame)
diff --git a/spec/websocket/extensions_spec.rb b/spec/websocket/extensions_spec.rb
index ccb305d..e850808 100644
--- a/spec/websocket/extensions_spec.rb
+++ b/spec/websocket/extensions_spec.rb
@@ -325,6 +325,16 @@
         expect(@extensions.generate_response("deflate, tar")).to eq "deflate; mode=compress"
       end
 
+      it "closes constructed sessions when response generation fails" do
+        allow(@nonconflict_session).to receive(:generate_response).and_raise(TypeError)
+        expect(@session).to receive(:close).exactly(1)
+        expect(@nonconflict_session).to receive(:close).exactly(1)
+
+        expect {
+          @extensions.generate_response("deflate, reverse")
+        }.to raise_error(TypeError)
+      end
+
       it "raises an error if the header is invalid" do
         expect { @extensions.generate_response("x-webkit- -frame") }.to raise_error(WebSocket::Extensions::Parser::ParseError)
       end