diff --git a/app/vmagent/remotewrite/client.go b/app/vmagent/remotewrite/client.go
index 0ebff6203d..e23a27aeba 100644
--- a/app/vmagent/remotewrite/client.go
+++ b/app/vmagent/remotewrite/client.go
@@ -151,12 +151,15 @@ func newHTTPClient(argIdx int, remoteWriteURL, sanitizedURL string, fq *persiste
 }
 
 func (c *client) init(argIdx, concurrency int, sanitizedURL string) {
+	// custom proto encoding is supported only over http connections
+	isHTTPClient := c.hc != nil
+
 	useVMProto := forceVMProto.GetOptionalArg(argIdx)
 	usePromProto := forcePromProto.GetOptionalArg(argIdx)
 	if useVMProto && usePromProto {
 		logger.Fatalf("-remoteWrite.useVMProto and -remoteWrite.usePromProto cannot be set simultaneously for -remoteWrite.url=%s", sanitizedURL)
 	}
-	if !useVMProto && !usePromProto {
+	if isHTTPClient && !useVMProto && !usePromProto {
 		// Auto-detect whether the remote storage supports VictoriaMetrics remote write protocol.
 		doRequest := func(url string) (*http.Response, error) {
 			return c.doRequest(url, nil)
@@ -167,7 +170,9 @@ func (c *client) init(argIdx, concurrency int, sanitizedURL string) {
 				"See https://docs.victoriametrics.com/vmagent.html#victoriametrics-remote-write-protocol", sanitizedURL)
 		}
 	}
-	c.useVMProto = useVMProto
+	if isHTTPClient {
+		c.useVMProto = useVMProto
+	}
 
 	if bytesPerSec := rateLimit.GetOptionalArgOrDefault(argIdx, 0); bytesPerSec > 0 {
 		logger.Infof("applying %d bytes per second rate limit for -remoteWrite.url=%q", bytesPerSec, sanitizedURL)