diff --git a/ChangeLog b/ChangeLog
index c2dea145e2..5f48b34925 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+Mon Mar 24 19:23:52 2008  Akinori MUSHA  <knu@iDaemons.org>
+
+	* parse.y (debug_lines): Always prepare a new array for each
+	  file's SCRIPT_LINES__ storage, instead of appending source lines
+	  every time a file is re-loaded; submitted by Rocky Bernstein in
+	  #18517.
+
 Mon Mar 24 10:25:54 2008  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* configure.in: sitearch should use target_cpu.  [ruby-core:15986]
diff --git a/parse.y b/parse.y
index 33aba9b6fa..8181c5c40a 100644
--- a/parse.y
+++ b/parse.y
@@ -4680,11 +4680,8 @@ debug_lines(const char *f)
 	VALUE hash = rb_const_get_at(rb_cObject, rb_intern("SCRIPT_LINES__"));
 	if (TYPE(hash) == T_HASH) {
 	    VALUE fname = rb_str_new2(f);
-	    VALUE lines = rb_hash_lookup(hash, fname);
-	    if (NIL_P(lines)) {
-		lines = rb_ary_new();
-		rb_hash_aset(hash, fname, lines);
-	    }
+	    VALUE lines = rb_ary_new();
+	    rb_hash_aset(hash, fname, lines);
 	    return lines;
 	}
     }