Index: ext/readline/readline.c
===================================================================
--- ext/readline/readline.c	(revision 18037)
+++ ext/readline/readline.c	(working copy)
@@ -511,6 +511,12 @@
 #endif /* HAVE_RL_FILENAME_QUOTE_CHARACTERS */
 }
 
+#ifdef HAVE_EDITLINE_READLINE_H
+#define HISTORY_BASE (history_base - 1)
+#else
+#define HISTORY_BASE (history_base)
+#endif
+
 static VALUE
 hist_to_s(self)
     VALUE self;
@@ -531,7 +537,7 @@
     if (i < 0) {
         i += history_length;
     }
-    entry = history_get(history_base + i);
+    entry = history_get(HISTORY_BASE + i);
     if (entry == NULL) {
 	rb_raise(rb_eIndexError, "invalid index");
     }
@@ -649,7 +655,7 @@
 
     rb_secure(4);
     for (i = 0; i < history_length; i++) {
-        entry = history_get(history_base + i);
+        entry = history_get(HISTORY_BASE + i);
         if (entry == NULL)
             break;
 	rb_yield(rb_tainted_str_new2(entry->line));