diff --git a/lib/saml2.coffee b/lib/saml2.coffee
index 09ac50e..a0d0f36 100644
--- a/lib/saml2.coffee
+++ b/lib/saml2.coffee
@@ -568,12 +568,16 @@ module.exports.ServiceProvider =
       xml = create_logout_request @entity_id, options.name_id, options.session_index, identity_provider.sso_logout_url
       zlib.deflateRaw xml, (err, deflated) =>
         return cb err if err?
-        uri = url.parse identity_provider.sso_logout_url
+        uri = url.parse identity_provider.sso_logout_url, true
+        query = null
         if options.sign_get_request
-          uri.query = sign_request deflated.toString('base64'), @private_key, options.relay_state
+          query = sign_request deflated.toString('base64'), @private_key, options.relay_state
         else
-          uri.query = SAMLRequest: deflated.toString 'base64'
-          uri.query.RelayState = options.relay_state if options.relay_state?
+          query = SAMLRequest: deflated.toString 'base64'
+          query.RelayState = options.relay_state if options.relay_state?
+        uri.query = _.extend(query, uri.query)
+        uri.search = null
+        uri.query = query
         cb null, url.format(uri)
 
     # Returns:
diff --git a/test/saml2.coffee b/test/saml2.coffee
index 3377a70..c7a62ea 100644
--- a/test/saml2.coffee
+++ b/test/saml2.coffee
@@ -624,6 +624,35 @@ describe 'saml2', ->
         assert parsed_url?.query?.Signature?, 'LogoutRequest is not signed'
         done()
 
+  it 'can create logout request url using an idp with query string parameter', (done) ->
+    sp_options =
+      entity_id: 'https://sp.example.com/metadata.xml'
+      private_key: get_test_file('test.pem')
+      certificate: get_test_file('test.crt')
+      assert_endpoint: 'https://sp.example.com/assert'
+    idp_options =
+      sso_login_url: 'https://idp.example.com/login'
+      sso_logout_url:  'https://idp.example.com?action=logout'
+      certificates: get_test_file('test.crt')
+    request_options =
+      name_id: 'name_id'
+      session_index: 'session_index'
+      sign_get_request: true
+
+    sp = new saml2.ServiceProvider sp_options
+    idp = new saml2.IdentityProvider idp_options
+
+    async.waterfall [
+      (cb_wf) -> sp.create_logout_request_url idp, request_options, cb_wf
+    ], (err, logout_url) ->
+      assert not err?, "Error creating logout URL: #{err}"
+      parsed_url = url.parse logout_url, true
+      console.log parsed_url
+      assert parsed_url?.query?.SAMLRequest?, 'Could not find SAMLRequest in url query parameters'
+      assert parsed_url?.query?.Signature?, 'LogoutRequest is not signed'
+      assert parsed_url?.query?.action?, 'Could not find action in url query parameters'
+      done()
+
     it 'can create logout request url using an string sso_logout_url', (done) ->
       sp_options =
         entity_id: 'https://sp.example.com/metadata.xml'