diff --git a/src/lj_api.c b/src/lj_api.c
index 1ad71678..548bef22 100644
--- a/src/lj_api.c
+++ b/src/lj_api.c
@@ -1297,6 +1297,9 @@ LUA_API int lua_gc(lua_State *L, int what, int data)
   case LUA_GCISRUNNING:
     res = (g->gc.threshold != LJ_MAX_MEM);
     break;
+  case LUA_GCESTIMATE:
+    res = (int)(g->gc.estimate >> 10);
+    break;
   default:
     res = -1;  /* Invalid option. */
   }
diff --git a/src/lua.h b/src/lua.h
index 6d1634d1..6655faad 100644
--- a/src/lua.h
+++ b/src/lua.h
@@ -228,6 +228,7 @@ LUA_API int  (lua_status) (lua_State *L);
 #define LUA_GCSETPAUSE		6
 #define LUA_GCSETSTEPMUL	7
 #define LUA_GCISRUNNING		9
+#define LUA_GCESTIMATE		10
 
 LUA_API int (lua_gc) (lua_State *L, int what, int data);