diff --git a/mix/CodeEditorExtensionManager.cpp b/mix/CodeEditorExtensionManager.cpp
index 79bbe9a9e..48c928a1f 100644
--- a/mix/CodeEditorExtensionManager.cpp
+++ b/mix/CodeEditorExtensionManager.cpp
@@ -114,6 +114,7 @@ void CodeEditorExtensionManager::setEditor(QQuickItem* _editor)
 
 void CodeEditorExtensionManager::onCodeChange()
 {
+	m_appContext->codeModel()->updateFormatting(m_doc); //update old formatting
 	m_appContext->codeModel()->registerCodeChange(m_doc->toPlainText());
 }
 
diff --git a/mix/CodeHighlighter.cpp b/mix/CodeHighlighter.cpp
index f246e9b7b..6476b0995 100644
--- a/mix/CodeHighlighter.cpp
+++ b/mix/CodeHighlighter.cpp
@@ -70,22 +70,25 @@ CodeHighlighter::FormatRange::FormatRange(CodeHighlighterSettings::Token _t, sol
 	token(_t), start(_location.start), length(_location.end - _location.start)
 {}
 
-void CodeHighlighter::processSource(solidity::Scanner* _scanner)
+void CodeHighlighter::processSource(std::string const& _source)
 {
-	solidity::Token::Value token = _scanner->getCurrentToken();
+	processComments(_source);
+	solidity::CharStream stream(_source);
+	solidity::Scanner scanner(stream);
+	solidity::Token::Value token = scanner.getCurrentToken();
 	while (token != Token::EOS)
 	{
 		if ((token >= Token::BREAK && token < Token::TYPES_END) ||
 				token == Token::IN || token == Token::DELETE || token == Token::NULL_LITERAL || token == Token::TRUE_LITERAL || token == Token::FALSE_LITERAL)
-			m_formats.push_back(FormatRange(CodeHighlighterSettings::Keyword, _scanner->getCurrentLocation()));
+			m_formats.push_back(FormatRange(CodeHighlighterSettings::Keyword, scanner.getCurrentLocation()));
 		else if (token == Token::STRING_LITERAL)
-			m_formats.push_back(FormatRange(CodeHighlighterSettings::StringLiteral, _scanner->getCurrentLocation()));
+			m_formats.push_back(FormatRange(CodeHighlighterSettings::StringLiteral, scanner.getCurrentLocation()));
 		else if (token == Token::COMMENT_LITERAL)
-			m_formats.push_back(FormatRange(CodeHighlighterSettings::Comment, _scanner->getCurrentLocation()));
+			m_formats.push_back(FormatRange(CodeHighlighterSettings::Comment, scanner.getCurrentLocation()));
 		else if (token == Token::NUMBER)
-			m_formats.push_back(FormatRange(CodeHighlighterSettings::NumLiteral, _scanner->getCurrentLocation()));
+			m_formats.push_back(FormatRange(CodeHighlighterSettings::NumLiteral, scanner.getCurrentLocation()));
 
-		token = _scanner->next();
+		token = scanner.next();
 	}
 	std::sort(m_formats.begin(), m_formats.end());
 }
@@ -98,6 +101,37 @@ void CodeHighlighter::processAST(solidity::ASTNode const& _ast)
 	std::sort(m_formats.begin(), m_formats.end());
 }
 
+
+void CodeHighlighter::processComments(std::string const& _source)
+{
+	unsigned i = 0;
+	unsigned size = _source.size();
+	if (size == 0)
+		return;
+	while (i < size - 1)
+	{
+		if (_source[i] == '/' && _source[i + 1] == '/')
+		{
+			//add single line comment
+			int start = i;
+			i += 2;
+			while (_source[i] != '\n' && i < size)
+				++i;
+			m_formats.push_back(FormatRange(CodeHighlighterSettings::Comment, start, i - start));
+		}
+		else if (_source[i] == '/' && _source[i + 1] == '*')
+		{
+			//add multiline comment
+			int start = i;
+			i += 2;
+			while ((_source[i] != '/' || _source[i - 1] != '*') && i < size)
+				++i;
+			m_formats.push_back(FormatRange(CodeHighlighterSettings::Comment, start, i - start + 1));
+		}
+		++i;
+	}
+}
+
 void CodeHighlighter::updateFormatting(QTextDocument* _document, CodeHighlighterSettings const& _settings)
 {
 	QTextBlock block = _document->firstBlock();
diff --git a/mix/CodeHighlighter.h b/mix/CodeHighlighter.h
index baf39bc66..8cc8b69e9 100644
--- a/mix/CodeHighlighter.h
+++ b/mix/CodeHighlighter.h
@@ -34,7 +34,6 @@ namespace dev
 namespace solidity
 {
 	class ASTNode;
-	class Scanner;
 	struct Location;
 }
 
@@ -81,10 +80,13 @@ public:
 
 public:
 	/// Collect highligting information
-	void processSource(solidity::Scanner* _scanner);
+	void processSource(std::string const& _source);
 	void processAST(solidity::ASTNode const& _ast);
 	void updateFormatting(QTextDocument* _document, CodeHighlighterSettings const& _settings);
 
+private:
+	void processComments(std::string const& _source);
+
 private:
 	Formats m_formats;
 };
diff --git a/mix/CodeModel.cpp b/mix/CodeModel.cpp
index 60c961045..deb58416c 100644
--- a/mix/CodeModel.cpp
+++ b/mix/CodeModel.cpp
@@ -24,7 +24,6 @@
 #include <QDebug>
 #include <QApplication>
 #include <QtQml>
-#include <libsolidity/Scanner.h>
 #include <libsolidity/CompilerStack.h>
 #include <libsolidity/SourceReferenceFormatter.h>
 #include <libevmcore/Instruction.h>
@@ -47,7 +46,8 @@ void BackgroundWorker::queueCodeChange(int _jobId, QString const& _content)
 CompilationResult::CompilationResult():
 	QObject(nullptr), m_successfull(false),
 	m_contract(new QContractDefinition()),
-	m_codeHighlighter(new CodeHighlighter())
+	m_codeHighlighter(new CodeHighlighter()),
+	m_codeHash(qHash(QString()))
 {}
 
 CompilationResult::CompilationResult(const solidity::CompilerStack& _compiler):
@@ -103,6 +103,9 @@ void CodeModel::stop()
 void CodeModel::registerCodeChange(const QString &_code)
 {
 	// launch the background thread
+	uint hash = qHash(_code);
+	if (m_result->m_codeHash == hash)
+		return;
 	m_backgroundJobId++;
 	m_compiling = true;
 	emit stateChanged();
@@ -121,9 +124,7 @@ void CodeModel::runCompilationJob(int _jobId, QString const& _code)
 	// run syntax highlighting first
 	// @todo combine this with compilation step
 	auto codeHighlighter = std::make_shared<CodeHighlighter>();
-	solidity::CharStream stream(source);
-	solidity::Scanner scanner(stream);
-	codeHighlighter->processSource(&scanner);
+	codeHighlighter->processSource(source);
 
 	// run compilation
 	try
@@ -139,9 +140,10 @@ void CodeModel::runCompilationJob(int _jobId, QString const& _code)
 		std::ostringstream error;
 		solidity::SourceReferenceFormatter::printExceptionInformation(error, _exception, "Error", cs);
 		result.reset(new CompilationResult(*m_result, QString::fromStdString(error.str())));
-		qDebug() << QString(QApplication::tr("compilation failed:") + " " + m_result->compilerMessage());
+		qDebug() << QString(QApplication::tr("compilation failed:") + " " + result->compilerMessage());
 	}
 	result->m_codeHighlighter = codeHighlighter;
+	result->m_codeHash = qHash(_code);
 
 	emit compilationCompleteInternal(result.release());
 }
diff --git a/mix/CodeModel.h b/mix/CodeModel.h
index d148cad87..da093183d 100644
--- a/mix/CodeModel.h
+++ b/mix/CodeModel.h
@@ -98,6 +98,7 @@ private:
 	std::shared_ptr<CodeHighlighter> m_codeHighlighter;
 	///@todo syntax highlighting, etc
 	friend class CodeModel;
+	uint m_codeHash;
 };
 
 /// Background code compiler
diff --git a/mix/qml/MainContent.qml b/mix/qml/MainContent.qml
index 0b3303aa8..99953344f 100644
--- a/mix/qml/MainContent.qml
+++ b/mix/qml/MainContent.qml
@@ -42,11 +42,11 @@ Rectangle {
                     anchors.centerIn: parent
                     tabChangesFocus: false
                     Keys.onPressed: {
-                            if (event.key === Qt.Key_Tab) {
-                                codeEditor.insert(codeEditor.cursorPosition, "\t");
-                                event.accepted = true;
-                            }
-                        }
+						if (event.key === Qt.Key_Tab) {
+							codeEditor.insert(codeEditor.cursorPosition, "\t");
+							event.accepted = true;
+						}
+					}
                 }
             }
             Rectangle {