diff -up lua-5.4.0/src/ldo.c.bug2 lua-5.4.0/src/ldo.c
--- lua-5.4.0/src/ldo.c.bug2	2020-07-31 10:40:55.409594540 -0400
+++ lua-5.4.0/src/ldo.c	2020-07-31 10:41:19.193556341 -0400
@@ -674,7 +674,7 @@ LUA_API int lua_resume (lua_State *L, lu
   if (from == NULL)
     L->nCcalls = CSTACKTHREAD;
   else  /* correct 'nCcalls' for this thread */
-    L->nCcalls = getCcalls(from) + from->nci - L->nci - CSTACKCF;
+    L->nCcalls = getCcalls(from) - L->nci - CSTACKCF;
   if (L->nCcalls <= CSTACKERR)
     return resume_error(L, "C stack overflow", nargs);
   luai_userstateresume(L, nargs);