diff --git a/lib/apache/master.rb b/lib/apache/master.rb
index f03d38d..12daa5d 100644
--- a/lib/apache/master.rb
+++ b/lib/apache/master.rb
@@ -2,6 +2,12 @@ module Apache
   # Options that aren't specific to a particular purpose go here. Once enough like methods for a
   # particular purpose exist, break them out into a separate module.
   module Master
+    class << self
+      def listening_on
+        @listening_on ||= []
+      end
+    end
+
     # Build a module list.
     # Wraps around Modules.build
     def modules(*modules, &block)
@@ -15,7 +21,14 @@ module Apache
     #    Listen "1.2.3.4:80"
     #    Listen "2.3.4.5:80"
     def listen(*opt)
-      opt.each { |adapter| self << "Listen #{adapter.quoteize}" }
+      opt.collect(&:quoteize).each do |adapter|
+        if !Apache::Master.listening_on.include?(adapter)
+          self << "Listen #{adapter}"
+          Apache::Master.listening_on << adapter
+        else
+          $stderr.puts "Multiple Listens for #{adapter}".foreground(:red)
+        end
+      end
     end
     alias :listen! :listen
 
diff --git a/spec/apache/master_spec.rb b/spec/apache/master_spec.rb
index f7bd8c0..ee77a14 100644
--- a/spec/apache/master_spec.rb
+++ b/spec/apache/master_spec.rb
@@ -1,4 +1,4 @@
-require 'apache/config'
+require 'spec_helper'
 
 describe Apache::Master, "should provide basic helpers for configuration" do
   let(:apache) { Apache::Config }
@@ -81,4 +81,16 @@ describe Apache::Master, "should provide basic helpers for configuration" do
     apache.set_header 'test3' => [ 'test4', "test5=test6" ]
     apache.to_a.should == [ 'Header set test test2', 'Header set "test3" "test4" test5=test6' ]
   end
+
+  describe '#listen' do
+    it 'should not allow one to listen twice on the same interface' do
+      apache.listen "one"
+      apache.listen "two"
+      apache.listen "one"
+
+      apache.to_a.should == [ 'Listen "one"', 'Listen "two"' ]
+
+      Apache::Master.listening_on.should == %w{"one" "two"}
+    end
+  end
 end