diff --git a/lib/roles/device.js b/lib/roles/device.js
index 0da81f0c..bf14666c 100644
--- a/lib/roles/device.js
+++ b/lib/roles/device.js
@@ -90,33 +90,23 @@ module.exports = function(options) {
       ])
     })
     .then(function() {
-      var port = 2870
-      return adb.openTcpAsync(options.serial, port)
-        .then(function(conn) {
-          conn.end()
-          throw new Error(util.format('Old connection still lives on port %d', port))
-        })
-        .catch(function(err) {
-            if (err.message === 'closed') {
-            return adb.shellAsync(options.serial, [
-                vendor.bin.dest
-              , '--lib', vendor.lib.dest
-              , '--listen-http', port
-              ])
-              .then(function(out) {
-                out.pipe(require('split')())
-                  .on('data', function(chunk) {
-                    log.info('remote: "%s"', chunk)
-                  })
-                  .on('end', function() {
-                    log.fatal('remote: Connection closed')
-                    selfDestruct()
-                  })
-              })
-          }
-          else {
-            throw err
-          }
+      return devutil.ensureUnusedPort(adb, options.serial, 2870)
+        .then(function(port) {
+          return adb.shellAsync(options.serial, [
+              vendor.bin.dest
+            , '--lib', vendor.lib.dest
+            , '--listen-http', port
+            ])
+            .then(function(out) {
+              out.pipe(require('split')())
+                .on('data', function(chunk) {
+                  log.info('remote: "%s"', chunk)
+                })
+                .on('end', function() {
+                  log.fatal('remote: Connection closed')
+                  selfDestruct()
+                })
+            })
         })
     })
     .done(function() {
diff --git a/lib/util/devutil.js b/lib/util/devutil.js
index 8eaa221d..736452bb 100644
--- a/lib/util/devutil.js
+++ b/lib/util/devutil.js
@@ -26,6 +26,20 @@ devutil.vendorFiles = function(identity) {
   }
 }
 
+devutil.ensureUnusedPort = function(adb, serial, port) {
+  function closedError(err) {
+    return err.message === 'closed'
+  }
+  return adb.openTcpAsync(serial, port)
+    .then(function(conn) {
+      conn.end()
+      throw new Error(util.format('Port "%d" should be unused', port))
+    })
+    .catch(closedError, function(err) {
+      return Promise.resolve(port)
+    })
+}
+
 devutil.killProcsByComm = function(adb, serial, comm, bin) {
   return adb.shellAsync(serial, ['ps', comm])
     .then(function(out) {