diff --git a/src/tar.c b/src/tar.c
index 1ee5ed41..1df9460c 100644
--- a/src/tar.c
+++ b/src/tar.c
@@ -2688,7 +2688,9 @@ decode_options (int argc, char **argv)
 			"please set it explicitly with --one-top-level=DIR"));
 	}
 
-      if (one_top_level_dir && !IS_RELATIVE_FILE_NAME (one_top_level_dir))
+      if (one_top_level_dir
+	  && ! (*one_top_level_dir
+		&& IS_RELATIVE_FILE_NAME (one_top_level_dir)))
 	paxusage(_("--one-top-level=DIR must use a relative file name"));
     }