diff --git a/ChangeLog b/ChangeLog
index dff7a703ef..be24cbbe66 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Thu Nov 29 16:14:41 2012  Koichi Sasada  <ko1@atdot.net>
+
+	* vm_backtrace.c (rb_debug_inspector_open): use RARRAY_LENINT() for
+	  int variable.
+
 Thu Nov 29 15:59:55 2012  Koichi Sasada  <ko1@atdot.net>
 
 	* include/ruby/debug.h: add rb_debug_inspector_* APIs.
diff --git a/vm_backtrace.c b/vm_backtrace.c
index a87cbc9fb2..de429ab44e 100644
--- a/vm_backtrace.c
+++ b/vm_backtrace.c
@@ -931,7 +931,7 @@ rb_debug_inspector_open(rb_debug_inspector_func_t func, void *data)
     dbg_context.th = th;
     dbg_context.cfp = dbg_context.th->cfp;
     dbg_context.backtrace = vm_backtrace_location_ary(th, 0, 0);
-    dbg_context.backtrace_size = RARRAY_LEN(dbg_context.backtrace);
+    dbg_context.backtrace_size = RARRAY_LENINT(dbg_context.backtrace);
     dbg_context.contexts = collect_caller_bindings(th);
 
     TH_PUSH_TAG(th);