3 files changed, 10 insertions, 2 deletions

diff --git a/lcorolib.c b/lcorolib.c
index 5b9736f1..23dd8441 100644
--- a/lcorolib.c
+++ b/lcorolib.c
@@ -190,6 +190,9 @@ static int luaB_close (lua_State *L) {
       }
     }
     case COS_RUN:  /* running coroutine? */
+      lua_geti(L, LUA_REGISTRYINDEX, LUA_RIDX_MAINTHREAD);  /* get main */
+      if (lua_tothread(L, -1) == co)
+        return luaL_error(L, "cannot close main thread");
       lua_closethread(co, L);  /* close itself */
       lua_assert(0);  /* previous call does not return */
       return 0;
diff --git a/manual/manual.of b/manual/manual.of
index 7c504d97..baa33d88 100644
--- a/manual/manual.of
+++ b/manual/manual.of
@@ -3284,8 +3284,8 @@ If @id{L} is equal to @id{from},
 it corresponds to a thread closing itself.
 In that case,
 the call does not return;
-instead, the resume or the protected call
-that (re)started the thread returns.
+instead, the resume that (re)started the thread returns.
+The thread must be running inside a resume.
 
 }
 
diff --git a/testes/coroutine.lua b/testes/coroutine.lua
index 02536ee5..4881d964 100644
--- a/testes/coroutine.lua
+++ b/testes/coroutine.lua
@@ -158,6 +158,11 @@ do
 
   local main = coroutine.running()
 
+  -- cannot close 'main'
+  local st, msg = pcall(coroutine.close, main);
+  assert(not st and string.find(msg, "main"))
+
+
   -- cannot close a "normal" coroutine
   ;(coroutine.wrap(function ()
     local st, msg = pcall(coroutine.close, main)