diff --git a/src/lapi_systemfs.cc b/src/lapi_systemfs.cc
index f299c89..66df405 100644
--- a/src/lapi_systemfs.cc
+++ b/src/lapi_systemfs.cc
@@ -15,10 +15,16 @@ namespace blt {
          int
          exists(lua_state* state)
          {
+            // Check arguments
+            if(lua_gettop(state) != 2)
+               luaL_error(state, "SystemFS:exists(path) takes a single argument, not %d arguments including SystemFS", lua_gettop(state));
+            if(!lua_isstring(state, -1))
+               luaL_error(state, "SystemFS:exists(path) -> argument 'path' must be a string!");
+
             // assuming PWD is base folder
-            const char* path = lua_tolstring(state, 1, NULL);
+            const char* path = lua_tolstring(state, -1, NULL);
             struct stat _stat;
-            lua_pushboolean(state, stat(path, &_stat));
+            lua_pushboolean(state, stat(path, &_stat) == 0);
             return 1;
          }
       }