diff --git a/packages/https-proxy/lib/server.coffee b/packages/https-proxy/lib/server.coffee
index a409774600..fe68de7265 100644
--- a/packages/https-proxy/lib/server.coffee
+++ b/packages/https-proxy/lib/server.coffee
@@ -139,6 +139,8 @@ class Server
 
       browserSocket.resume()
 
+    port or= "443"
+
     if upstreamProxy = @_getProxyForUrl("https://#{hostname}:#{port}")
       # todo: as soon as all requests are intercepted, this can go away since this is just for pass-through
       debug("making proxied connection %o", {
diff --git a/packages/https-proxy/test/unit/server_spec.coffee b/packages/https-proxy/test/unit/server_spec.coffee
index acf7f51440..4cfcfa19be 100644
--- a/packages/https-proxy/test/unit/server_spec.coffee
+++ b/packages/https-proxy/test/unit/server_spec.coffee
@@ -43,33 +43,56 @@ describe "lib/server", ->
       socket.destroy = @sandbox.stub()
       head = {}
 
-      onError = (err, socket, head, port) ->
+      onError = (err, socket2, head2, port) ->
         expect(err.message).to.eq("connect ECONNREFUSED 127.0.0.1:8444")
 
-        expect(socket).to.eq(socket)
-        expect(head).to.eq(head)
+        expect(socket).to.eq(socket2)
+        expect(head).to.eq(head2)
         expect(port).to.eq("8444")
 
         expect(socket.destroy).to.be.calledOnce
 
         done()
 
-      @setup({onError: onError})
+      @setup({ onError })
       .then (srv) ->
         conn = srv._makeDirectConnection({url: "localhost:8444"}, socket, head)
 
       return
 
+    ## https://github.com/cypress-io/cypress/issues/3250
+    it "does not crash when an erroneous URL is provided, just destroys socket", (done) ->
+      socket = new EE()
+      socket.destroy = @sandbox.stub()
+      head = {}
+
+      onError = (err, socket2, head2, port) ->
+        expect(err.message).to.eq("connect ECONNREFUSED 127.0.0.1:443")
+
+        expect(socket).to.eq(socket2)
+        expect(head).to.eq(head2)
+        expect(port).to.eq("443")
+
+        expect(socket.destroy).to.be.calledOnce
+
+        done()
+
+      @setup({ onError })
+      .then (srv) ->
+        conn = srv._makeDirectConnection({url: "%7Balgolia_application_id%7D-dsn.algolia.net:443"}, socket, head)
+
+      return
+
     it "with proxied connection calls options.onError with err and port and destroys the client socket", (done) ->
       socket = new EE()
       socket.destroy = @sandbox.stub()
       head = {}
 
-      onError = (err, socket, head, port) ->
+      onError = (err, socket2, head2, port) ->
         expect(err.message).to.eq("A connection to the upstream proxy could not be established: connect ECONNREFUSED 127.0.0.1:8444")
 
-        expect(socket).to.eq(socket)
-        expect(head).to.eq(head)
+        expect(socket).to.eq(socket2)
+        expect(head).to.eq(head2)
         expect(port).to.eq("11111")
 
         expect(socket.destroy).to.be.calledOnce
@@ -79,7 +102,7 @@ describe "lib/server", ->
       process.env.HTTPS_PROXY = 'http://localhost:8444'
       process.env.NO_PROXY = ''
 
-      @setup({onError: onError})
+      @setup({ onError })
       .then (srv) ->
         conn = srv._makeDirectConnection({url: "should-not-reach.invalid:11111"}, socket, head)