diff --git a/libsolidity/analysis/ConstantEvaluator.h b/libsolidity/analysis/ConstantEvaluator.h
index 0f2dd558e..e92113bb8 100644
--- a/libsolidity/analysis/ConstantEvaluator.h
+++ b/libsolidity/analysis/ConstantEvaluator.h
@@ -54,11 +54,11 @@ public:
 	TypePointer evaluate(Expression const& _expr);
 
 private:
-	virtual void endVisit(BinaryOperation const& _operation);
-	virtual void endVisit(UnaryOperation const& _operation);
-	virtual void endVisit(Literal const& _literal);
-	virtual void endVisit(Identifier const& _identifier);
-	virtual void endVisit(TupleExpression const& _tuple);
+	void endVisit(BinaryOperation const& _operation) override;
+	void endVisit(UnaryOperation const& _operation) override;
+	void endVisit(Literal const& _literal) override;
+	void endVisit(Identifier const& _identifier) override;
+	void endVisit(TupleExpression const& _tuple) override;
 
 	void setType(ASTNode const& _node, TypePointer const& _type);
 	TypePointer type(ASTNode const& _node);
diff --git a/libsolidity/analysis/StaticAnalyzer.h b/libsolidity/analysis/StaticAnalyzer.h
index f3ed30b20..57ac54fb1 100644
--- a/libsolidity/analysis/StaticAnalyzer.h
+++ b/libsolidity/analysis/StaticAnalyzer.h
@@ -50,7 +50,7 @@ class StaticAnalyzer: private ASTConstVisitor
 public:
 	/// @param _errorReporter provides the error logging functionality.
 	explicit StaticAnalyzer(langutil::ErrorReporter& _errorReporter);
-	~StaticAnalyzer();
+	~StaticAnalyzer() override;
 
 	/// Performs static analysis on the given source unit and all of its sub-nodes.
 	/// @returns true iff all checks passed. Note even if all checks passed, errors() can still contain warnings
diff --git a/libyul/backends/evm/EVMAssembly.h b/libyul/backends/evm/EVMAssembly.h
index e4ba4979a..744d8738b 100644
--- a/libyul/backends/evm/EVMAssembly.h
+++ b/libyul/backends/evm/EVMAssembly.h
@@ -38,7 +38,7 @@ class EVMAssembly: public AbstractAssembly
 {
 public:
 	explicit EVMAssembly(bool _evm15 = false): m_evm15(_evm15) { }
-	virtual ~EVMAssembly() = default;
+	~EVMAssembly() override = default;
 
 	/// Set a new source location valid starting from the next instruction.
 	void setSourceLocation(langutil::SourceLocation const& _location) override;
diff --git a/libyul/backends/evm/EVMCodeTransform.h b/libyul/backends/evm/EVMCodeTransform.h
index fb4bc38e1..eae870815 100644
--- a/libyul/backends/evm/EVMCodeTransform.h
+++ b/libyul/backends/evm/EVMCodeTransform.h
@@ -92,10 +92,10 @@ public:
 	{}
 
 public:
-	void operator()(Identifier const& _identifier);
-	void operator()(FunctionDefinition const&);
-	void operator()(ForLoop const&);
-	void operator()(Block const& _block);
+	void operator()(Identifier const& _identifier) override;
+	void operator()(FunctionDefinition const&) override;
+	void operator()(ForLoop const&) override;
+	void operator()(Block const& _block) override;
 
 private:
 	void increaseRefIfFound(YulString _variableName);
diff --git a/libyul/backends/evm/NoOutputAssembly.h b/libyul/backends/evm/NoOutputAssembly.h
index bc914f9ac..d72f9ea66 100644
--- a/libyul/backends/evm/NoOutputAssembly.h
+++ b/libyul/backends/evm/NoOutputAssembly.h
@@ -45,7 +45,7 @@ class NoOutputAssembly: public AbstractAssembly
 {
 public:
 	explicit NoOutputAssembly(bool _evm15 = false): m_evm15(_evm15) { }
-	virtual ~NoOutputAssembly() = default;
+	~NoOutputAssembly() override = default;
 
 	void setSourceLocation(langutil::SourceLocation const&) override {}
 	int stackHeight() const override { return m_stackHeight; }
diff --git a/libyul/optimiser/ASTCopier.h b/libyul/optimiser/ASTCopier.h
index 0ac0b5f82..3a05d2ca3 100644
--- a/libyul/optimiser/ASTCopier.h
+++ b/libyul/optimiser/ASTCopier.h
@@ -65,7 +65,7 @@ public:
 class ASTCopier: public ExpressionCopier, public StatementCopier
 {
 public:
-	virtual ~ASTCopier() = default;
+	~ASTCopier() override = default;
 	Expression operator()(Literal const& _literal) override;
 	Expression operator()(Identifier const& _identifier) override;
 	Expression operator()(FunctionCall const&) override;
diff --git a/libyul/optimiser/ExpressionSimplifier.h b/libyul/optimiser/ExpressionSimplifier.h
index c11ab9bf3..ce83b4e1e 100644
--- a/libyul/optimiser/ExpressionSimplifier.h
+++ b/libyul/optimiser/ExpressionSimplifier.h
@@ -46,7 +46,7 @@ public:
 	static void run(OptimiserStepContext&, Block& _ast);
 
 	using ASTModifier::operator();
-	virtual void visit(Expression& _expression);
+	void visit(Expression& _expression) override;
 
 private:
 	explicit ExpressionSimplifier(Dialect const& _dialect): DataFlowAnalyzer(_dialect) {}
diff --git a/libyul/optimiser/FunctionHoister.h b/libyul/optimiser/FunctionHoister.h
index 2a88e1acf..7106c03a4 100644
--- a/libyul/optimiser/FunctionHoister.h
+++ b/libyul/optimiser/FunctionHoister.h
@@ -42,7 +42,7 @@ public:
 	static void run(OptimiserStepContext&, Block& _ast) { FunctionHoister{}(_ast); }
 
 	using ASTModifier::operator();
-	virtual void operator()(Block& _block);
+	void operator()(Block& _block) override;
 
 private:
 	FunctionHoister() = default;
diff --git a/libyul/optimiser/NameCollector.cpp b/libyul/optimiser/NameCollector.cpp
index 33a5b624a..f9bb40bf4 100644
--- a/libyul/optimiser/NameCollector.cpp
+++ b/libyul/optimiser/NameCollector.cpp
@@ -36,9 +36,9 @@ void NameCollector::operator()(VariableDeclaration const& _varDecl)
 void NameCollector::operator ()(FunctionDefinition const& _funDef)
 {
 	m_names.emplace(_funDef.name);
-	for (auto const arg: _funDef.parameters)
+	for (auto const& arg: _funDef.parameters)
 		m_names.emplace(arg.name);
-	for (auto const ret: _funDef.returnVariables)
+	for (auto const& ret: _funDef.returnVariables)
 		m_names.emplace(ret.name);
 	ASTWalker::operator ()(_funDef);
 }
diff --git a/libyul/optimiser/NameCollector.h b/libyul/optimiser/NameCollector.h
index 97fbd27c6..a48aa1a3b 100644
--- a/libyul/optimiser/NameCollector.h
+++ b/libyul/optimiser/NameCollector.h
@@ -61,8 +61,8 @@ public:
 	{}
 
 	using ASTWalker::operator ();
-	virtual void operator()(Identifier const& _identifier);
-	virtual void operator()(FunctionCall const& _funCall);
+	void operator()(Identifier const& _identifier) override;
+	void operator()(FunctionCall const& _funCall) override;
 
 	static std::map<YulString, size_t> countReferences(Block const& _block, CountWhat _countWhat = VariablesAndFunctions);
 	static std::map<YulString, size_t> countReferences(FunctionDefinition const& _function, CountWhat _countWhat = VariablesAndFunctions);
diff --git a/libyul/optimiser/Semantics.h b/libyul/optimiser/Semantics.h
index 4efc83247..46d2984ca 100644
--- a/libyul/optimiser/Semantics.h
+++ b/libyul/optimiser/Semantics.h
@@ -104,7 +104,7 @@ public:
 	static bool containsMSize(Dialect const& _dialect, Block const& _ast);
 
 	using ASTWalker::operator();
-	void operator()(FunctionCall const& _funCall);
+	void operator()(FunctionCall const& _funCall) override;
 
 private:
 	MSizeFinder(Dialect const& _dialect): m_dialect(_dialect) {}
@@ -129,7 +129,7 @@ public:
 	}
 
 	using ASTWalker::operator();
-	void operator()(Leave const&) { m_leaveFound = true; }
+	void operator()(Leave const&) override { m_leaveFound = true; }
 
 private:
 	LeaveFinder() = default;
diff --git a/libyul/optimiser/TypeInfo.cpp b/libyul/optimiser/TypeInfo.cpp
index ea2d81a83..adb6e1cce 100644
--- a/libyul/optimiser/TypeInfo.cpp
+++ b/libyul/optimiser/TypeInfo.cpp
@@ -50,12 +50,12 @@ public:
 		ASTWalker::operator()(_funDef);
 
 		auto& funType = functionTypes[_funDef.name];
-		for (auto const arg: _funDef.parameters)
+		for (auto const& arg: _funDef.parameters)
 		{
 			funType.parameters.emplace_back(arg.type);
 			variableTypes[arg.name] = arg.type;
 		}
-		for (auto const ret: _funDef.returnVariables)
+		for (auto const& ret: _funDef.returnVariables)
 		{
 			funType.returns.emplace_back(ret.type);
 			variableTypes[ret.name] = ret.type;
diff --git a/test/libsolidity/SMTChecker.cpp b/test/libsolidity/SMTChecker.cpp
index 06862ad08..6df19c1c7 100644
--- a/test/libsolidity/SMTChecker.cpp
+++ b/test/libsolidity/SMTChecker.cpp
@@ -34,14 +34,14 @@ namespace solidity::frontend::test
 class SMTCheckerFramework: public AnalysisFramework
 {
 protected:
-	virtual std::pair<SourceUnit const*, ErrorList>
+	std::pair<SourceUnit const*, ErrorList>
 	parseAnalyseAndReturnError(
 		std::string const& _source,
 		bool _reportWarnings = false,
 		bool _insertVersionPragma = true,
 		bool _allowMultipleErrors = false,
 		bool _allowRecoveryErrors = false
-	)
+	) override
 	{
 		return AnalysisFramework::parseAnalyseAndReturnError(
 			"pragma experimental SMTChecker;\n" + _source,
diff --git a/test/libsolidity/SolidityExecutionFramework.h b/test/libsolidity/SolidityExecutionFramework.h
index aaa17525f..2410195fa 100644
--- a/test/libsolidity/SolidityExecutionFramework.h
+++ b/test/libsolidity/SolidityExecutionFramework.h
@@ -46,7 +46,7 @@ public:
 		ExecutionFramework(_evmVersion), m_showMetadata(solidity::test::CommonOptions::get().showMetadata)
 	{}
 
-	virtual bytes const& compileAndRunWithoutCheck(
+	bytes const& compileAndRunWithoutCheck(
 		std::string const& _sourceCode,
 		u256 const& _value = 0,
 		std::string const& _contractName = "",
diff --git a/test/libsolidity/SolidityExpressionCompiler.cpp b/test/libsolidity/SolidityExpressionCompiler.cpp
index cdaee104b..5dfefc0b7 100644
--- a/test/libsolidity/SolidityExpressionCompiler.cpp
+++ b/test/libsolidity/SolidityExpressionCompiler.cpp
@@ -52,15 +52,15 @@ public:
 	FirstExpressionExtractor(ASTNode& _node): m_expression(nullptr) { _node.accept(*this); }
 	Expression* expression() const { return m_expression; }
 private:
-	virtual bool visit(Assignment& _expression) override { return checkExpression(_expression); }
-	virtual bool visit(UnaryOperation& _expression) override { return checkExpression(_expression); }
-	virtual bool visit(BinaryOperation& _expression) override { return checkExpression(_expression); }
-	virtual bool visit(FunctionCall& _expression) override { return checkExpression(_expression); }
-	virtual bool visit(MemberAccess& _expression) override { return checkExpression(_expression); }
-	virtual bool visit(IndexAccess& _expression) override { return checkExpression(_expression); }
-	virtual bool visit(Identifier& _expression) override { return checkExpression(_expression); }
-	virtual bool visit(ElementaryTypeNameExpression& _expression) override { return checkExpression(_expression); }
-	virtual bool visit(Literal& _expression) override { return checkExpression(_expression); }
+	bool visit(Assignment& _expression) override { return checkExpression(_expression); }
+	bool visit(UnaryOperation& _expression) override { return checkExpression(_expression); }
+	bool visit(BinaryOperation& _expression) override { return checkExpression(_expression); }
+	bool visit(FunctionCall& _expression) override { return checkExpression(_expression); }
+	bool visit(MemberAccess& _expression) override { return checkExpression(_expression); }
+	bool visit(IndexAccess& _expression) override { return checkExpression(_expression); }
+	bool visit(Identifier& _expression) override { return checkExpression(_expression); }
+	bool visit(ElementaryTypeNameExpression& _expression) override { return checkExpression(_expression); }
+	bool visit(Literal& _expression) override { return checkExpression(_expression); }
 	bool checkExpression(Expression& _expression)
 	{
 		if (m_expression == nullptr)
diff --git a/test/libsolidity/SolidityParser.cpp b/test/libsolidity/SolidityParser.cpp
index 192a26898..12fbc3fce 100644
--- a/test/libsolidity/SolidityParser.cpp
+++ b/test/libsolidity/SolidityParser.cpp
@@ -672,7 +672,7 @@ BOOST_AUTO_TEST_CASE(inline_asm_end_location)
 	{
 	public:
 		bool visited = false;
-		virtual bool visit(InlineAssembly const& _inlineAsm)
+		bool visit(InlineAssembly const& _inlineAsm) override
 		{
 			auto loc = _inlineAsm.location();
 			auto asmStr = loc.source->source().substr(loc.start, loc.end - loc.start);
diff --git a/test/libyul/SyntaxTest.h b/test/libyul/SyntaxTest.h
index b4c838b54..342aa2845 100644
--- a/test/libyul/SyntaxTest.h
+++ b/test/libyul/SyntaxTest.h
@@ -37,7 +37,7 @@ public:
 		return std::make_unique<SyntaxTest>(_config.filename, _config.evmVersion);
 	}
 	SyntaxTest(std::string const& _filename, langutil::EVMVersion _evmVersion);
-	virtual ~SyntaxTest() {}
+	~SyntaxTest() override {}
 protected:
 	void parseAndAnalyze() override;
 
diff --git a/tools/solidityUpgrade/Upgrade050.h b/tools/solidityUpgrade/Upgrade050.h
index d85b69912..58670e7b2 100644
--- a/tools/solidityUpgrade/Upgrade050.h
+++ b/tools/solidityUpgrade/Upgrade050.h
@@ -37,7 +37,7 @@ public:
 
 	void analyze(frontend::SourceUnit const& _sourceUnit) { _sourceUnit.accept(*this); }
 private:
-	void endVisit(frontend::ContractDefinition const& _contract);
+	void endVisit(frontend::ContractDefinition const& _contract) override;
 };
 
 /**
@@ -52,7 +52,7 @@ public:
 
 	void analyze(frontend::SourceUnit const& _sourceUnit) { _sourceUnit.accept(*this); }
 private:
-	void endVisit(frontend::FunctionDefinition const& _function);
+	void endVisit(frontend::FunctionDefinition const& _function) override;
 };
 
 }
diff --git a/tools/solidityUpgrade/Upgrade060.h b/tools/solidityUpgrade/Upgrade060.h
index ea29d3a7b..e2386d104 100644
--- a/tools/solidityUpgrade/Upgrade060.h
+++ b/tools/solidityUpgrade/Upgrade060.h
@@ -35,7 +35,7 @@ public:
 
 	void analyze(frontend::SourceUnit const& _sourceUnit) { _sourceUnit.accept(*this); }
 private:
-	void endVisit(frontend::ContractDefinition const& _contract);
+	void endVisit(frontend::ContractDefinition const& _contract) override;
 };
 
 /**
@@ -49,7 +49,7 @@ public:
 
 	void analyze(frontend::SourceUnit const& _sourceUnit) { _sourceUnit.accept(*this); }
 private:
-	void endVisit(frontend::ContractDefinition const& _contract);
+	void endVisit(frontend::ContractDefinition const& _contract) override;
 };
 
 /**
@@ -63,7 +63,7 @@ public:
 
 	void analyze(frontend::SourceUnit const& _sourceUnit) { _sourceUnit.accept(*this); }
 private:
-	void endVisit(frontend::ContractDefinition const& _function);
+	void endVisit(frontend::ContractDefinition const& _function) override;
 };
 
 }