diff --git a/string.c b/string.c
index 2759aaa94a..c8deba7234 100644
--- a/string.c
+++ b/string.c
@@ -6467,7 +6467,7 @@ str_undump(VALUE str)
 	rb_raise(rb_eRuntimeError, "non-ASCII character detected");
     }
     if (!str_null_check(str, &w)) {
-       rb_raise(rb_eRuntimeError, "string contains null byte");
+	rb_raise(rb_eRuntimeError, "string contains null byte");
     }
     if (RSTRING_LEN(str) < 2) goto invalid_format;
     if (*s != '"') goto invalid_format;