diff --git a/backend/src/lexer.cpp b/backend/src/lexer.cpp
index cab8ca1..8980500 100644
--- a/backend/src/lexer.cpp
+++ b/backend/src/lexer.cpp
@@ -212,7 +212,7 @@ bool CommandShowLexer(const std::string &command, std::string &ISBN,
                       std::string &name, std::string &author,
                       std::string &keyword) {
   static std::basic_regex main_pattern(
-      R"(^ *show(?: +-ISBN=(?:\S{1,20})| +-name=\"(?:[^\s"]{1,60})\"| +-author=\"(?:[^\s"]{1,60})\"| +-keyword=\"(?:[^\s"]{1,60})\")* *$)",
+      R"(^ *show(?: +-ISBN=(?:\S{1,20})| +-name=\"(?:[^\s"]{1,60})\"| +-author=\"(?:[^\s"]{1,60})\"| +-keyword=\"(?:[^\s"]{1,60})\")? *$)",
       std::regex_constants::optimize);
 
   bool has_ISBN = false;