diff --git a/common/lc_category.cpp b/common/lc_category.cpp
index 83de802b..3899f423 100644
--- a/common/lc_category.cpp
+++ b/common/lc_category.cpp
@@ -184,7 +184,7 @@ bool lcMatchCategory(const char* PieceName, const char* Expression)
 		}
 		else if ((*p == '|') || (*p == '&'))
 		{
-			std::string LeftStr(Expression, (p - Expression) - 1);
+			std::string LeftStr(Expression, std::max(p - Expression, static_cast<ptrdiff_t>(1)) - 1);
 			std::string RightStr(p + 1);
 
 			if (*p == '|')
@@ -258,6 +258,9 @@ bool lcMatchCategory(const char* PieceName, const char* Expression)
 		Word++;
 	}
 
+	if (!Word[0])
+		return false;
+
 	const char* Result = strcasestr(PieceName, Word);
 
 	if (!Result)