diff --git a/socketserver/server/backend.go b/socketserver/server/backend.go
index b0684c64..62fccd16 100644
--- a/socketserver/server/backend.go
+++ b/socketserver/server/backend.go
@@ -142,7 +142,7 @@ func (backend *backendInfo) SendRemoteCommand(remoteCommand, data string, auth A
 	} else if resp.StatusCode < 200 || resp.StatusCode > 299 { // any non-2xx
 		// If the Content-Type header includes a charset, ignore it.
 		typeStr := resp.Header.Get("Content-Type")
-		splitIdx := strings.Index(typeStr, ";")
+		splitIdx := strings.IndexRune(typeStr, ';')
 		if ( splitIdx != -1 ) {
 			typeStr = strings.TrimSpace(typeStr[0:splitIdx])
 		}