diff --git a/x264.c b/x264.c
index 7d98518..bf2b3ee 100644
--- a/x264.c
+++ b/x264.c
@@ -933,9 +933,9 @@ static int select_output( const char *muxer, char *filename, x264_param_t *param
 static int select_input( const char *demuxer, char *used_demuxer, char *filename,
                          hnd_t *p_handle, video_info_t *info, cli_input_opt_t *opt )
 {
-    const char *ext = get_filename_extension( filename );
-    int b_regular = strcmp( filename, "-" );
     int b_auto = !strcasecmp( demuxer, "auto" );
+    const char *ext = b_auto ? get_filename_extension( filename ) : "";
+    int b_regular = strcmp( filename, "-" );
     if( !b_regular && b_auto )
         ext = "raw";
     b_regular = b_regular && x264_is_regular_file_path( filename );