--- a/src/lparser.c
+++ b/src/lparser.c
@@ -301,6 +301,7 @@
     expdesc key;
     singlevaraux(fs, ls->envn, var, 1);  /* get environment variable */
     lua_assert(var->k == VLOCAL || var->k == VUPVAL);
+    luaK_exp2anyregup(fs, var);  /* but could be a constant */
     codestring(ls, &key, varname);  /* key is variable name */
     luaK_indexed(fs, var, &key);  /* env[varname] */
   }