diff --git a/mix/HttpServer.cpp b/mix/HttpServer.cpp
index 977008ead..968580907 100644
--- a/mix/HttpServer.cpp
+++ b/mix/HttpServer.cpp
@@ -110,7 +110,10 @@ void HttpServer::updateListening()
 		return;
 
 	if (!QTcpServer::listen(QHostAddress::LocalHost, m_port))
+	{
 		errorStringChanged();
+		return;
+	}
 
 	if (m_port != QTcpServer::serverPort())
 	{
diff --git a/mix/qml/WebPreview.qml b/mix/qml/WebPreview.qml
index bd1d37e61..44f96a775 100644
--- a/mix/qml/WebPreview.qml
+++ b/mix/qml/WebPreview.qml
@@ -40,11 +40,14 @@ Item {
 		var contracts = {};
 		for (var c in codeModel.contracts) {
 			var contract = codeModel.contracts[c];
-			contracts[c] = {
-				name: contract.contract.name,
-				address: clientModel.contractAddresses[contract.contract.name],
-				interface: JSON.parse(contract.contractInterface),
-			};
+			var address = clientModel.contractAddresses[contract.contract.name];
+			if (address) {
+				contracts[c] = {
+					name: contract.contract.name,
+					address: address,
+					interface: JSON.parse(contract.contractInterface),
+				};
+			}
 		}
 		webView.runJavaScript("updateContracts(" + JSON.stringify(contracts) + ")");
 	}
diff --git a/mix/test/qml/TestMain.qml b/mix/test/qml/TestMain.qml
index ef1af0c53..73cff824e 100644
--- a/mix/test/qml/TestMain.qml
+++ b/mix/test/qml/TestMain.qml
@@ -50,12 +50,21 @@ TestCase
 
 	function editContract(c)
 	{
+		if (mainApplication.codeModel.compiling)
+			ts.waitForSignal(mainApplication.codeModel, "compilationComplete()", 5000);
 		mainApplication.mainContent.codeEditor.getEditor("contract.sol").setText(c);
 		if (!ts.waitForSignal(mainApplication.codeModel, "compilationComplete()", 5000))
 			fail("not compiled");
 		ts.keyPressChar(mainApplication, "S", Qt.ControlModifier, 200); //Ctrl+S
 	}
 
+
+	function waitForExecution()
+	{
+		while (mainApplication.clientModel.running)
+			ts.waitForSignal(mainApplication.clientModel, "runComplete()", 5000);
+	}
+
 	function editHtml(c)
 	{
 		mainApplication.projectModel.openDocument("index.html");
diff --git a/mix/test/qml/js/TestDebugger.js b/mix/test/qml/js/TestDebugger.js
index b5b923f45..706601d18 100644
--- a/mix/test/qml/js/TestDebugger.js
+++ b/mix/test/qml/js/TestDebugger.js
@@ -14,8 +14,7 @@ function test_defaultTransactionSequence()
 	"	uint z;\r" +
 	"}\r"
 	);
-	if (!ts.waitForSignal(mainApplication.clientModel, "runComplete()", 5000))
-		fail("Error running transaction");
+	waitForExecution();
 	tryCompare(mainApplication.mainContent.rightPane.transactionLog.transactionModel, "count", 3);
 }
 
@@ -47,8 +46,7 @@ function test_transactionWithParameter()
 	transactionDialog.acceptAndClose();
 	mainApplication.projectModel.stateDialog.acceptAndClose();
 	mainApplication.mainContent.startQuickDebugging();
-	if (!ts.waitForSignal(mainApplication.clientModel, "runComplete()", 5000))
-		fail("Error running transaction");
+	waitForExecution();
 	tryCompare(mainApplication.mainContent.rightPane.transactionLog.transactionModel, "count", 5);
 	tryCompare(mainApplication.mainContent.rightPane.transactionLog.transactionModel.get(4), "returned", "(442)");
 }
@@ -79,8 +77,7 @@ function test_constructorParameters()
 	transactionDialog.acceptAndClose();
 	mainApplication.projectModel.stateDialog.acceptAndClose();
 	mainApplication.mainContent.startQuickDebugging();
-	if (!ts.waitForSignal(mainApplication.clientModel, "runComplete()", 5000))
-		fail("Error running transaction");
+	waitForExecution();
 	tryCompare(mainApplication.mainContent.rightPane.transactionLog.transactionModel, "count", 4);
 	tryCompare(mainApplication.mainContent.rightPane.transactionLog.transactionModel.get(3), "returned", "(442)");
 }
diff --git a/mix/test/qml/js/TestProject.js b/mix/test/qml/js/TestProject.js
index 7f149eff4..444760ea3 100644
--- a/mix/test/qml/js/TestProject.js
+++ b/mix/test/qml/js/TestProject.js
@@ -4,8 +4,7 @@ function test_contractRename()
 	tryCompare(mainApplication.mainContent.projectNavigator.sections.itemAt(0).model.get(0), "name", "Contract");
 	editContract("contract Renamed {}");
 	mainApplication.mainContent.startQuickDebugging();
-	if (!ts.waitForSignal(mainApplication.clientModel, "runComplete()", 5000))
-		fail("Error running transaction");
+	waitForExecution();
 	wait(1000);
 	tryCompare(mainApplication.mainContent.projectNavigator.sections.itemAt(0).model.get(0), "name", "Renamed");
 	mainApplication.projectModel.stateListModel.editState(0);