diff --git a/vendor/github.com/prometheus/client_golang/prometheus/promhttp/delegator.go b/vendor/github.com/prometheus/client_golang/prometheus/promhttp/delegator.go
index fa53568..e7c0d05 100644
--- a/vendor/github.com/prometheus/client_golang/prometheus/promhttp/delegator.go
+++ b/vendor/github.com/prometheus/client_golang/prometheus/promhttp/delegator.go
@@ -53,15 +53,21 @@
 }
 
 func (r *responseWriterDelegator) WriteHeader(code int) {
+	if r.observeWriteHeader != nil && !r.wroteHeader {
+		// Only call observeWriteHeader for the 1st time. It's a bug if
+		// WriteHeader is called more than once, but we want to protect
+		// against it here. Note that we still delegate the WriteHeader
+		// to the original ResponseWriter to not mask the bug from it.
+		r.observeWriteHeader(code)
+	}
 	r.status = code
 	r.wroteHeader = true
 	r.ResponseWriter.WriteHeader(code)
-	if r.observeWriteHeader != nil {
-		r.observeWriteHeader(code)
-	}
 }
 
 func (r *responseWriterDelegator) Write(b []byte) (int, error) {
+	// If applicable, call WriteHeader here so that observeWriteHeader is
+	// handled appropriately.
 	if !r.wroteHeader {
 		r.WriteHeader(http.StatusOK)
 	}
@@ -77,17 +83,23 @@
 type pusherDelegator struct{ *responseWriterDelegator }
 
 func (d closeNotifierDelegator) CloseNotify() <-chan bool {
-	//lint:ignore SA1019 http.CloseNotifier is deprecated but we don't want to
-	//remove support from client_golang yet.
+	//nolint:staticcheck // Ignore SA1019. http.CloseNotifier is deprecated but we keep it here to not break existing users.
 	return d.ResponseWriter.(http.CloseNotifier).CloseNotify()
 }
 func (d flusherDelegator) Flush() {
+	// If applicable, call WriteHeader here so that observeWriteHeader is
+	// handled appropriately.
+	if !d.wroteHeader {
+		d.WriteHeader(http.StatusOK)
+	}
 	d.ResponseWriter.(http.Flusher).Flush()
 }
 func (d hijackerDelegator) Hijack() (net.Conn, *bufio.ReadWriter, error) {
 	return d.ResponseWriter.(http.Hijacker).Hijack()
 }
 func (d readerFromDelegator) ReadFrom(re io.Reader) (int64, error) {
+	// If applicable, call WriteHeader here so that observeWriteHeader is
+	// handled appropriately.
 	if !d.wroteHeader {
 		d.WriteHeader(http.StatusOK)
 	}
@@ -335,8 +347,7 @@
 	}
 
 	id := 0
-	//lint:ignore SA1019 http.CloseNotifier is deprecated but we don't want to
-	//remove support from client_golang yet.
+	//nolint:staticcheck // Ignore SA1019. http.CloseNotifier is deprecated but we keep it here to not break existing users.
 	if _, ok := w.(http.CloseNotifier); ok {
 		id += closeNotifier
 	}