diff --git a/string.c b/string.c
index 050ef27d9b..e9204fc233 100644
--- a/string.c
+++ b/string.c
@@ -3077,7 +3077,10 @@ rb_str_prepend_multi(int argc, VALUE *argv, VALUE str)
 {
     str_modifiable(str);
 
-    if (argc > 0) {
+    if (argc == 1) {
+	rb_str_update(str, 0L, 0L, argv[0]);
+    }
+    else if (argc > 1) {
 	int i;
 	VALUE arg_str = rb_str_tmp_new(0);
 	rb_enc_copy(arg_str, str);