diff --git a/modules/caddyhttp/reverseproxy/caddyfile.go b/modules/caddyhttp/reverseproxy/caddyfile.go
index fcaf82b9dc6..193487a04af 100644
--- a/modules/caddyhttp/reverseproxy/caddyfile.go
+++ b/modules/caddyhttp/reverseproxy/caddyfile.go
@@ -155,7 +155,9 @@ func (h *Handler) UnmarshalCaddyfile(d *caddyfile.Dispenser) error {
 			if err != nil {
 				host = upstreamAddr
 			}
-			if port == "" {
+			// we can assume a port if only a hostname is specified, but use of a
+			// placeholder without a port likely means a port will be filled in
+			if port == "" && !strings.Contains(host, "{") {
 				port = "80"
 			}
 		}