diff --git a/code/debug-info.lisp b/code/debug-info.lisp
index b80becf3fde9ed7b81ca6affa459cbc44ee612b6..0c8983dd7c3b06ea606fab2b1962d1f57837f300 100644
--- a/code/debug-info.lisp
+++ b/code/debug-info.lisp
@@ -98,6 +98,7 @@
 	      (res `(make-string ,len)))
     `(progn
        (%primitive byte-blt ,vec ,index ,res 0 ,len)
+       (incf ,index ,len)
        ,res)))