diff --git a/ide/CellModel.cpp b/ide/CellModel.cpp
index 8271c87..0aa29bb 100644
--- a/ide/CellModel.cpp
+++ b/ide/CellModel.cpp
@@ -147,6 +147,11 @@
     addCell(Cell(code, result));
 }
 
+void CellModel::insertCellBefore(int index)
+{
+    insertRow(index);
+}
+
 void CellModel::announceCellChange(Cell *cell, int role)
 {
     // TODO: Optimize
diff --git a/ide/CellModel.h b/ide/CellModel.h
index 1f56056..428422a 100644
--- a/ide/CellModel.h
+++ b/ide/CellModel.h
@@ -44,6 +44,8 @@
     Q_INVOKABLE void addCell(const Cell &cell);
     Q_INVOKABLE void addCell(QString code, QString result);
 
+    Q_INVOKABLE void insertCellBefore(int index);
+
 private:
     Notebook *_notebook;
     void announceCellChange(Cell *cell, int role);
diff --git a/ide/NbRuntime.cpp b/ide/NbRuntime.cpp
index 8454597..35df413 100644
--- a/ide/NbRuntime.cpp
+++ b/ide/NbRuntime.cpp
@@ -2,10 +2,12 @@
 
 #include "NbRuntime.h"
 #include "../Parser.h"
+#include "../StdLib.h"
 
 NbRuntime::NbRuntime(QObject *parent)
     : QThread(parent)
 {
+    StdLib().load(_eval);
 }
 
 void NbRuntime::queueCell(Cell *cell)
@@ -118,5 +120,10 @@
             _running = nullptr;
             emit cellFinishedRunning(cell, RuntimeResult(ex));
         }
+        catch (AssertionException &ex)
+        {
+            _running = nullptr;
+            emit cellFinishedRunning(cell, RuntimeResult(ex));
+        }
     }
 }
diff --git a/ide/Notebook.cpp b/ide/Notebook.cpp
index 82bee7e..953e98b 100644
--- a/ide/Notebook.cpp
+++ b/ide/Notebook.cpp
@@ -2,6 +2,8 @@
 #include "CellModel.h"
 #include "../PPrint.h"
 
+// TODO: avoid potential race condition if Cell is deleted, pass by value with same UUID instead
+
 Notebook::Notebook(QObject *parent)
     : QObject(parent)
     , _cellModel(new CellModel(this))
diff --git a/ide/qml/main.qml b/ide/qml/main.qml
index bf99a8d..ef6134a 100644
--- a/ide/qml/main.qml
+++ b/ide/qml/main.qml
@@ -76,7 +76,7 @@
                     }
 
                     InsertRow {
-                        onInsertClicked: notebook.cellModel.insertRows(notebook.cellModel.index(0, 0), 1);
+                        onInsertClicked: notebook.cellModel.insertCellBefore(0)
                     }
                 }
 
@@ -86,7 +86,6 @@
                     required property var model
                     required property var index
                     required property var uuid
-                    required property int status
 
                     width: codeEditor.width - 5
 
@@ -98,7 +97,7 @@
 
                     onInsertBelowClicked: {
                         console.info(index);
-                        notebook.cellModel.insertRows(notebook.cellModel.index(index + 1, 0), 1);
+                        notebook.cellModel.insertCellBefore(index + 1);
                     }
 
                     onRunClicked: {