diff --git a/middleware/proxy/proxy_test.go b/middleware/proxy/proxy_test.go
index aab836bc..55abe2dc 100644
--- a/middleware/proxy/proxy_test.go
+++ b/middleware/proxy/proxy_test.go
@@ -98,11 +98,6 @@ func TestWebSocketReverseProxyFromWSClient(t *testing.T) {
 // also sets up the rules/environment for testing WebSocket
 // proxy.
 func newWebSocketTestProxy(backendAddr string) *Proxy {
-	proxyHeaders = http.Header{
-		"Connection": {"{>Connection}"},
-		"Upgrade":    {"{>Upgrade}"},
-	}
-
 	return &Proxy{
 		Upstreams: []Upstream{&fakeUpstream{name: backendAddr}},
 	}
@@ -121,7 +116,9 @@ func (u *fakeUpstream) Select() *UpstreamHost {
 	return &UpstreamHost{
 		Name:         u.name,
 		ReverseProxy: NewSingleHostReverseProxy(uri, ""),
-		ExtraHeaders: proxyHeaders,
+		ExtraHeaders: http.Header{
+			"Connection": {"{>Connection}"},
+			"Upgrade":    {"{>Upgrade}"}},
 	}
 }
 
diff --git a/middleware/proxy/upstream.go b/middleware/proxy/upstream.go
index 7916b3b6..5e9152e4 100644
--- a/middleware/proxy/upstream.go
+++ b/middleware/proxy/upstream.go
@@ -16,13 +16,13 @@ import (
 
 var (
 	supportedPolicies = make(map[string]func() Policy)
-	proxyHeaders      = make(http.Header)
 )
 
 type staticUpstream struct {
-	from   string
-	Hosts  HostPool
-	Policy Policy
+	from         string
+	proxyHeaders http.Header
+	Hosts        HostPool
+	Policy       Policy
 
 	FailTimeout time.Duration
 	MaxFails    int32
@@ -72,7 +72,7 @@ func NewStaticUpstreams(c parse.Dispenser) ([]Upstream, error) {
 				Fails:        0,
 				FailTimeout:  upstream.FailTimeout,
 				Unhealthy:    false,
-				ExtraHeaders: proxyHeaders,
+				ExtraHeaders: upstream.proxyHeaders,
 				CheckDown: func(upstream *staticUpstream) UpstreamHostDownFunc {
 					return func(uh *UpstreamHost) bool {
 						if uh.Unhealthy {
@@ -159,10 +159,16 @@ func parseBlock(c *parse.Dispenser, u *staticUpstream) error {
 		if !c.Args(&header, &value) {
 			return c.ArgErr()
 		}
-		proxyHeaders.Add(header, value)
+		if u.proxyHeaders == nil {
+			u.proxyHeaders = make(http.Header)
+		}
+		u.proxyHeaders.Add(header, value)
 	case "websocket":
-		proxyHeaders.Add("Connection", "{>Connection}")
-		proxyHeaders.Add("Upgrade", "{>Upgrade}")
+		if u.proxyHeaders == nil {
+			u.proxyHeaders = make(http.Header)
+		}
+		u.proxyHeaders.Add("Connection", "{>Connection}")
+		u.proxyHeaders.Add("Upgrade", "{>Upgrade}")
 	case "without":
 		if !c.NextArg() {
 			return c.ArgErr()