diff --git a/inc/expression.hpp b/inc/expression.hpp
index 5e6a345..811ae8c 100644
--- a/inc/expression.hpp
+++ b/inc/expression.hpp
@@ -302,11 +302,12 @@ public:
 		 // if value, left and right hands should be null
 
 	explicit TreeNode(void)
+		: l(nullptr), r(nullptr), o()
 	{
 	}
 
 	explicit TreeNode(const Token t)
-		: o(t)
+		: l(nullptr), r(nullptr), o(t)
 	{
 	}
 
diff --git a/src/parser.cpp b/src/parser.cpp
index 9049b25..7ec7573 100644
--- a/src/parser.cpp
+++ b/src/parser.cpp
@@ -377,7 +377,10 @@ void print_token_vector(const std::vector<Expression::Token>& tv)
 		std::cout << "(" << *tv[i].to_str() << ") ";
 	}
 
-	std::cout << "(" << *tv[i].to_str() << ")\n";
+	if (tv.size())
+	{
+		std::cout << "(" << *tv[i].to_str() << ")\n";
+	}
 }
 
 void print_math_vector(const std::vector<Expression::Token>& tv)
@@ -388,7 +391,10 @@ void print_math_vector(const std::vector<Expression::Token>& tv)
 		std::cout << *tv[i].to_math_str(); //<< " ";
 	}
 
-	std::cout << *tv[i].to_math_str() << "\n";
+	if (tv.size())
+	{
+		std::cout << *tv[i].to_math_str() << "\n";
+	}
 }
 
 }
diff --git a/src/syntaxer.cpp b/src/syntaxer.cpp
index 6efb778..0c33b7f 100644
--- a/src/syntaxer.cpp
+++ b/src/syntaxer.cpp
@@ -35,6 +35,7 @@ int check_syntax(std::vector<Expression::Token>& tv)
 	int problem_cnt = 0;
 
 	// check start and finish validity
+	if (tv.size())
 	{
 		int pc = problem_cnt;
 
@@ -101,6 +102,7 @@ int check_syntax(std::vector<Expression::Token>& tv)
 	}
 
 	// check token type sequence
+	if (tv.size() > 1)
 	{
 		for (int i = 0, l = tv.size() - 1, pc; pc = problem_cnt, i < l; i++)
 		{
@@ -812,7 +814,11 @@ Expression::TreeNode ov_to_tree(const std::vector<Expression::Token> tv, const s
 {
 	Expression::TreeNode root;
 	std::queue<std::pair<Expression::TreeNode *, int>> queued_ops;
-	queued_ops.emplace(&root, ov.size() - 1);
+
+	if (ov.size())
+	{
+		queued_ops.emplace(&root, ov.size() - 1);
+	}
 
 	while (queued_ops.size())
 	{