diff --git a/lib/index.js b/lib/index.js
index 5287e4ead0..183e3e1b05 100644
--- a/lib/index.js
+++ b/lib/index.js
@@ -358,10 +358,11 @@ Server.prototype.serve = function(req, res){
   // Per the standard, ETags must be quoted:
   // https://tools.ietf.org/html/rfc7232#section-2.3
   var expectedEtag = '"' + clientVersion + '"';
+  var weakEtag = 'W/' + expectedEtag;
 
   var etag = req.headers['if-none-match'];
   if (etag) {
-    if (expectedEtag == etag) {
+    if (expectedEtag == etag || weakEtag == etag) {
       debug('serve client 304');
       res.writeHead(304);
       res.end();
diff --git a/test/socket.io.js b/test/socket.io.js
index aec781455e..88e1b5ed62 100644
--- a/test/socket.io.js
+++ b/test/socket.io.js
@@ -182,6 +182,19 @@ describe('socket.io', function(){
         });
       });
 
+      it('should handle 304 from weak etag', function(done){
+        var srv = http();
+        io(srv);
+        request(srv)
+            .get('/socket.io/socket.io.js')
+            .set('If-None-Match', 'W/"' + clientVersion + '"')
+            .end(function(err, res){
+              if (err) return done(err);
+              expect(res.statusCode).to.be(304);
+              done();
+            });
+      });
+
       it('should not serve static files', function(done){
         var srv = http();
         io(srv, { serveClient: false });