diff --git a/luprex/cpp/core/source.cpp b/luprex/cpp/core/source.cpp
index 30e4f615..a2e3abdc 100644
--- a/luprex/cpp/core/source.cpp
+++ b/luprex/cpp/core/source.cpp
@@ -582,6 +582,7 @@ bool SourceDB::search_docs(const eng::string &substring, std::ostream &ostream)
     // Search the built-in functions.
     for (const LuaFunctionReg *reg = LuaFunctionReg::All; reg != nullptr; reg=reg->next()) {
         eng::string proto = get_reg_prototype(reg);
+        if (reg->get_sandbox()) continue;
         if (sv::contains_substring_utf8(proto, substring) ||
             sv::contains_substring_utf8(reg->get_docs(), substring)) {
             ostream << proto;