diff --git a/builtin/difftool.c b/builtin/difftool.c
index 42ad9e804a..b5e85ab079 100644
--- a/builtin/difftool.c
+++ b/builtin/difftool.c
@@ -567,7 +567,7 @@ static int run_dir_diff(const char *extcmd, int symlinks, const char *prefix,
 				warning(_("both files modified: '%s' and '%s'."),
 					wtdir.buf, rdir.buf);
 				warning(_("working tree file has been left."));
-				warning("");
+				warning("%s", "");
 				err = 1;
 			} else if (unlink(wtdir.buf) ||
 				   copy_file(wtdir.buf, rdir.buf, st.st_mode))