diff --git a/lib/websocket/extensions.rb b/lib/websocket/extensions.rb
index 14ca7ab..3bcc5ae 100644
--- a/lib/websocket/extensions.rb
+++ b/lib/websocket/extensions.rb
@@ -67,6 +67,7 @@ def generate_offer
       end
 
       @sessions = sessions
+      @client_sessions = sessions
       @index    = index
 
       offer.size > 0 ? offer.join(', ') : nil
@@ -157,7 +158,10 @@ def process_outgoing_message(message)
     def close
       return unless @sessions
 
-      @sessions.each do |ext, session|
+      sessions = @client_sessions || @sessions
+      @client_sessions, @sessions = nil, []
+
+      sessions.each do |ext, session|
         session.close rescue nil
       end
     end
diff --git a/spec/websocket/extensions_spec.rb b/spec/websocket/extensions_spec.rb
index ccb305d..39f00b7 100644
--- a/spec/websocket/extensions_spec.rb
+++ b/spec/websocket/extensions_spec.rb
@@ -161,6 +161,22 @@
       end
     end
 
+    describe :close do
+      before do
+        @extensions.add(@nonconflict)
+        @extensions.generate_offer
+        @extensions.activate("deflate")
+      end
+
+      it "closes selected and unselected sessions only once" do
+        expect(@session).to receive(:close).exactly(1)
+        expect(@nonconflict_session).to receive(:close).exactly(1)
+
+        @extensions.close
+        @extensions.close
+      end
+    end
+
     describe :process_incoming_message do
       before do
         @extensions.add(@conflict)