diff --git a/core/config.go b/core/config.go
index 8f2018e64fd3..3ab2a3765652 100644
--- a/core/config.go
+++ b/core/config.go
@@ -64,7 +64,11 @@ func GetMergedConfig(args cmdarg.Arg) (string, error) {
 	var files []*ConfigSource
 	supported := []string{"json", "yaml", "toml"}
 	for _, file := range args {
-		format := GetFormat(file)
+		format := "json"
+		if file != "stdin:" {
+			format = GetFormat(file)
+		}
+
 		if slices.Contains(supported, format) {
 			files = append(files, &ConfigSource{
 				Name:   file,