diff --git a/mrbgems/mruby-array-ext/src/array.c b/mrbgems/mruby-array-ext/src/array.c
index e138bb793..0b8dcb3c9 100644
--- a/mrbgems/mruby-array-ext/src/array.c
+++ b/mrbgems/mruby-array-ext/src/array.c
@@ -307,10 +307,10 @@ ary_rotate_bang(mrb_state *mrb, mrb_value self)
 
   struct RArray *a = mrb_ary_ptr(self);
   mrb_int len = ARY_LEN(a);
-  mrb_value *p = ARY_PTR(a);
   mrb_int idx;
 
   mrb_ary_modify(mrb, a);
+  mrb_value *p = ARY_PTR(a);
   if (len == 0 || count == 0) return self;
   if (count == 1) {
     mrb_value v = p[0];