diff --git a/NEWS.md b/NEWS.md
index 07a77aa8..849cf000 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -7,6 +7,7 @@ Enhancements:
  - Upgrade windshaft to 0.19.2, see node_modules/windshaft/NEWS
  - Clarify obscure "ECONNREFUSED" error message (#171)
  - Change some http status responses to be more appropriate to the case
+ - Forbid using map signatures of foreign users (#173)
 
 1.8.3 -- 2014-02-27
 -------------------
diff --git a/lib/cartodb/server_options.js b/lib/cartodb/server_options.js
index f32d0835..a153cb8a 100644
--- a/lib/cartodb/server_options.js
+++ b/lib/cartodb/server_options.js
@@ -718,6 +718,12 @@ module.exports = function(){
           if ( tksplit.length > 1 ) {
             req.params.signer = tksplit.shift();
             if ( ! req.params.signer ) req.params.signer = user;
+            else if ( req.params.signer != user ) {
+              var err = new Error('Cannot use map signature of user "' + req.params.signer + '" on database of user "' + user + '"')
+              err.http_status = 403;
+              callback(err);
+              return;
+            }
             if ( tksplit.length > 1 ) {
               var template_hash = tksplit.shift(); // unused
             }
diff --git a/test/acceptance/templates.js b/test/acceptance/templates.js
index b411836f..a93f5700 100644
--- a/test/acceptance/templates.js
+++ b/test/acceptance/templates.js
@@ -865,7 +865,7 @@ suite('template_api', function() {
             "Missing 'error' from response body: " + res.body);
           assert.ok(parsed.error.match(/permission denied/i),
             'Unexpected error for unauthorized instance '
-            + '(expected /permission denied): ' + parsed.error);
+            + '(expected /permission denied/): ' + parsed.error);
           var get_request = {
               url: '/tiles/layergroup/' + layergroupid + '/0/0/0.png?auth_token=valid1',
               method: 'GET',
@@ -884,6 +884,33 @@ suite('template_api', function() {
           assert.equal(res.headers['content-type'], "image/png");
           return null;
         },
+        // See https://github.com/CartoDB/Windshaft-cartodb/issues/172
+        function fetchTileForeignSignature(err, res) {
+          if ( err ) throw err;
+          var foreignsigned = layergroupid.replace(/[^@]*@/, 'foreign@');
+          var get_request = {
+              url: '/tiles/layergroup/' + foreignsigned + '/0/0/0.png?auth_token=valid1',
+              method: 'GET',
+              headers: {host: 'localhost' },
+              encoding: 'binary'
+          }
+          var next = this;
+          assert.response(server, get_request, {},
+            function(res) { next(null, res); });
+        },
+        function checkForeignSignerError(err, res) {
+          if ( err ) throw err;
+          assert.equal(res.statusCode, 403, 
+            'Unexpected error for authorized instance: '
+            + res.statusCode + ' -- ' + res.body);
+          var parsed = JSON.parse(res.body);
+          assert.ok(parsed.hasOwnProperty('error'),
+            "Missing 'error' from response body: " + res.body);
+          assert.ok(parsed.error.match(/cannot use/i),
+            'Unexpected error for unauthorized instance '
+            + '(expected /cannot use/): ' + parsed.error);
+          return null;
+        },
         function deleteTemplate(err)
         {
           if ( err ) throw err;