diff --git a/apps/Makefile b/apps/Makefile
index 2a34edc13..815800ced 100644
--- a/apps/Makefile
+++ b/apps/Makefile
@@ -7,6 +7,7 @@ include apps/calculation/Makefile
 app_objs += $(addprefix apps/,\
   apps_container.o\
   constant.o\
+  expression_text_field_delegate.o\
   main.o\
 )
 
diff --git a/apps/calculation/app.cpp b/apps/calculation/app.cpp
index 4c2867583..25ccffc53 100644
--- a/apps/calculation/app.cpp
+++ b/apps/calculation/app.cpp
@@ -8,7 +8,7 @@ App::App(Context * context) :
   m_globalContext(context),
   m_calculationStore(CalculationStore()),
   m_historyController(HistoryController(&m_editExpressionController, &m_calculationStore)),
-  m_editExpressionController(EditExpressionController(&m_modalViewController, &m_historyController, &m_calculationStore))
+  m_editExpressionController(EditExpressionController(&m_modalViewController, &m_historyController, &m_calculationStore, this))
 {
 }
 
diff --git a/apps/calculation/app.h b/apps/calculation/app.h
index 35553e85f..863fcfd8c 100644
--- a/apps/calculation/app.h
+++ b/apps/calculation/app.h
@@ -3,11 +3,12 @@
 
 #include "edit_expression_controller.h"
 #include "history_controller.h"
+#include "../expression_text_field_delegate.h"
 #include <escher.h>
 
 namespace Calculation {
 
-class App : public ::App {
+class App : public ::App, public ExpressionTextFieldDelegate {
 public:
   App(Context * context);
   Context * globalContext();
diff --git a/apps/calculation/edit_expression_controller.cpp b/apps/calculation/edit_expression_controller.cpp
index 9fc3c7b8b..45864ec15 100644
--- a/apps/calculation/edit_expression_controller.cpp
+++ b/apps/calculation/edit_expression_controller.cpp
@@ -4,10 +4,10 @@
 
 namespace Calculation {
 
-EditExpressionController::ContentView::ContentView(TableView * subview) :
+EditExpressionController::ContentView::ContentView(TableView * subview, TextFieldDelegate * textFieldDelegate) :
   View(),
   m_mainView(subview),
-  m_textField(nullptr, m_textBody, 255)
+  m_textField(nullptr, m_textBody, 255, textFieldDelegate)
 {
   m_textBody[0] = 0;
 }
@@ -43,9 +43,9 @@ TableView * EditExpressionController::ContentView::mainView() {
   return m_mainView;
 }
 
-EditExpressionController::EditExpressionController(Responder * parentResponder, HistoryController * historyController, CalculationStore * calculationStore) :
+EditExpressionController::EditExpressionController(Responder * parentResponder, HistoryController * historyController, CalculationStore * calculationStore, TextFieldDelegate * textFieldDelegate) :
   ViewController(parentResponder),
-  m_contentView((TableView *)historyController->view()),
+  m_contentView((TableView *)historyController->view(), textFieldDelegate),
   m_historyController(historyController),
   m_calculationStore(calculationStore)
 {
diff --git a/apps/calculation/edit_expression_controller.h b/apps/calculation/edit_expression_controller.h
index a47f8112f..533a68993 100644
--- a/apps/calculation/edit_expression_controller.h
+++ b/apps/calculation/edit_expression_controller.h
@@ -10,7 +10,7 @@ class HistoryController;
 
 class EditExpressionController : public ViewController {
 public:
-  EditExpressionController(Responder * parentResponder, HistoryController * historyController, CalculationStore * calculationStore);
+  EditExpressionController(Responder * parentResponder, HistoryController * historyController, CalculationStore * calculationStore, TextFieldDelegate * textFieldDelegate);
   View * view() override;
   const char * title() const override;
   void didBecomeFirstResponder() override;
@@ -21,7 +21,7 @@ public:
 private:
   class ContentView : public View {
   public:
-    ContentView(TableView * subview);
+    ContentView(TableView * subview, TextFieldDelegate * textFieldDelegate);
     int numberOfSubviews() const override;
     View * subviewAtIndex(int index) override;
     void layoutSubviews() override;
diff --git a/apps/expression_text_field_delegate.cpp b/apps/expression_text_field_delegate.cpp
new file mode 100644
index 000000000..a591baa2a
--- /dev/null
+++ b/apps/expression_text_field_delegate.cpp
@@ -0,0 +1,13 @@
+#include "expression_text_field_delegate.h"
+#include <poincare.h>
+
+bool ExpressionTextFieldDelegate::textFieldDidReceiveEvent(TextField * textField, Ion::Events::Event event) {
+  if (event == Ion::Events::Event::ENTER && Expression::parse(textField->textBuffer()) == nullptr) {
+    if (textField->bufferLength() == 0) {
+      return true;
+    }
+    textField->app()->displayWarning("Attention a la syntaxe jeune padawan");
+    return true;
+  }
+  return false;
+}
diff --git a/apps/expression_text_field_delegate.h b/apps/expression_text_field_delegate.h
new file mode 100644
index 000000000..c21aa3f5d
--- /dev/null
+++ b/apps/expression_text_field_delegate.h
@@ -0,0 +1,11 @@
+#ifndef APPS_EXPRESSION_TEXT_FIELD_DELEGATE_H
+#define APPS_EXPRESSION_TEXT_FIELD_DELEGATE_H
+
+#include <escher.h>
+
+class ExpressionTextFieldDelegate : public TextFieldDelegate {
+public:
+  bool textFieldDidReceiveEvent(TextField * textField, Ion::Events::Event event) override;
+};
+
+#endif
diff --git a/apps/graph/app.cpp b/apps/graph/app.cpp
index aea5a71d4..3611dd320 100644
--- a/apps/graph/app.cpp
+++ b/apps/graph/app.cpp
@@ -14,7 +14,7 @@ App::App(::Context * context) :
   m_valuesController(nullptr, &m_functionStore, &m_evaluateContext),
   m_valuesStackViewController(StackViewController(&m_tabViewController, &m_valuesController)),
   m_tabViewController(&m_inputViewController, &m_listStackViewController, &m_graphController, &m_valuesStackViewController),
-  m_inputViewController(&m_modalViewController, &m_tabViewController)
+  m_inputViewController(&m_modalViewController, &m_tabViewController, this)
 {
 }
 
diff --git a/apps/graph/app.h b/apps/graph/app.h
index dd7894eac..a0b4b462e 100644
--- a/apps/graph/app.h
+++ b/apps/graph/app.h
@@ -7,10 +7,11 @@
 #include "graph/graph_controller.h"
 #include "list/list_controller.h"
 #include "values/values_controller.h"
+#include "../expression_text_field_delegate.h"
 
 namespace Graph {
 
-class App : public ::App {
+class App : public ::App, public ExpressionTextFieldDelegate {
 public:
   App(::Context * context);
   InputViewController * inputViewController();
diff --git a/escher/include/escher.h b/escher/include/escher.h
index 36b671309..16daa2425 100644
--- a/escher/include/escher.h
+++ b/escher/include/escher.h
@@ -30,6 +30,7 @@
 #include <escher/switch_view.h>
 #include <escher/switch_menu_list_cell.h>
 #include <escher/text_field.h>
+#include <escher/text_field_delegate.h>
 #include <escher/text_menu_list_cell.h>
 #include <escher/text_view.h>
 #include <escher/tab_view_controller.h>
diff --git a/escher/include/escher/input_view_controller.h b/escher/include/escher/input_view_controller.h
index 22c1dbdfe..27ccbf3bd 100644
--- a/escher/include/escher/input_view_controller.h
+++ b/escher/include/escher/input_view_controller.h
@@ -4,10 +4,11 @@
 #include <escher/view_controller.h>
 #include <escher/invocation.h>
 #include <escher/text_field.h>
+#include <escher/text_field_delegate.h>
 
 class InputViewController : public ViewController {
 public:
-  InputViewController(Responder * parentResponder, ViewController * child);
+  InputViewController(Responder * parentResponder, ViewController * child, TextFieldDelegate * textFieldDelegate = nullptr);
   View * view() override;
   const char * title() const override;
 
@@ -17,7 +18,7 @@ public:
 private:
   class ContentView : public View {
   public:
-    ContentView();
+    ContentView(TextFieldDelegate * textFieldDelegate);
     void setMainView(View * subview);
     int numberOfSubviews() const override;
     View * subviewAtIndex(int index) override;
diff --git a/escher/include/escher/text_field.h b/escher/include/escher/text_field.h
index 23aef242a..26b7e682d 100644
--- a/escher/include/escher/text_field.h
+++ b/escher/include/escher/text_field.h
@@ -3,17 +3,19 @@
 
 #include <escher/view.h>
 #include <escher/responder.h>
+#include <escher/text_field_delegate.h>
 #include <string.h>
 
 class TextField : public View, public Responder {
 public:
-  TextField(Responder * parentResponder, char * textBuffer, size_t textBufferSize);
+  TextField(Responder * parentResponder, char * textBuffer, size_t textBufferSize, TextFieldDelegate * delegate = nullptr);
   // View
   void drawRect(KDContext * ctx, KDRect rect) const override;
   // Responder
   bool handleEvent(Ion::Events::Event event) override;
 
   const char * textBuffer() const;
+  int bufferLength() const;
   void setTextBuffer(const char * text);
 protected:
 #if ESCHER_VIEW_LOGGING
@@ -23,6 +25,7 @@ private:
   char * m_textBuffer;
   size_t m_textBufferSize;
   size_t m_currentTextLength;
+  TextFieldDelegate * m_delegate;
 };
 
 #endif
diff --git a/escher/include/escher/text_field_delegate.h b/escher/include/escher/text_field_delegate.h
new file mode 100644
index 000000000..8630e61c7
--- /dev/null
+++ b/escher/include/escher/text_field_delegate.h
@@ -0,0 +1,11 @@
+#ifndef ESCHER_TEXT_FIELD_DELEGATE_H
+#define ESCHER_TEXT_FIELD_DELEGATE_H
+
+class TextField;
+
+class TextFieldDelegate {
+public:
+  virtual bool textFieldDidReceiveEvent(TextField * textField, Ion::Events::Event event) = 0;
+};
+
+#endif
diff --git a/escher/src/input_view_controller.cpp b/escher/src/input_view_controller.cpp
index b09b9712d..5e817f657 100644
--- a/escher/src/input_view_controller.cpp
+++ b/escher/src/input_view_controller.cpp
@@ -2,10 +2,10 @@
 #include <escher/app.h>
 #include <assert.h>
 
-InputViewController::ContentView::ContentView() :
+InputViewController::ContentView::ContentView(TextFieldDelegate * textFieldDelegate) :
   View(),
   m_mainView(nullptr),
-  m_textField(nullptr, m_textBody, 255),
+  m_textField(nullptr, m_textBody, 255, textFieldDelegate),
   m_visibleInput(false)
 {
   m_textBody[0] = 0;
@@ -61,9 +61,9 @@ TextField * InputViewController::ContentView::textField() {
   return &m_textField;
 }
 
-InputViewController::InputViewController(Responder * parentResponder, ViewController * child) :
+InputViewController::InputViewController(Responder * parentResponder, ViewController * child, TextFieldDelegate * textFieldDelegate) :
   ViewController(parentResponder),
-  m_contentView(),
+  m_contentView(textFieldDelegate),
   m_previousResponder(nullptr),
   m_regularViewController(child),
   m_successAction(Invocation(nullptr, nullptr)),
diff --git a/escher/src/text_field.cpp b/escher/src/text_field.cpp
index b3987ff1f..cd9c72981 100644
--- a/escher/src/text_field.cpp
+++ b/escher/src/text_field.cpp
@@ -1,11 +1,12 @@
 #include <escher/text_field.h>
 
-TextField::TextField(Responder * parentResponder, char * textBuffer, size_t textBufferSize) :
+TextField::TextField(Responder * parentResponder, char * textBuffer, size_t textBufferSize, TextFieldDelegate * delegate) :
   View(),
   Responder(parentResponder),
   m_textBuffer(textBuffer),
   m_textBufferSize(textBufferSize),
-  m_currentTextLength(0)
+  m_currentTextLength(0),
+  m_delegate(delegate)
 {
 }
 
@@ -25,27 +26,36 @@ const char * TextField::className() const {
 /* Responder */
 
 bool TextField::handleEvent(Ion::Events::Event event) {
-  if (event == Ion::Events::Event::DELETE && m_currentTextLength > 0) {
-    KDSize sizePreviousText = KDText::stringSize(m_textBuffer);
-    m_currentTextLength--;
-    m_textBuffer[m_currentTextLength] = 0;
-    KDSize sizeText = KDText::stringSize(m_textBuffer);
-    KDRect dirtyZone(sizeText.width(), 0, sizePreviousText.width()-sizeText.width(), sizeText.height());
-    markRectAsDirty(dirtyZone);
-    return true;
+  if (m_delegate) {
+    if (m_delegate->textFieldDidReceiveEvent(this, event)) {
+      return true;
+    }
   }
-  if ((int)event >= 0x100) {
-    return false;
+  switch (event) {
+    case Ion::Events::Event::DELETE:
+      if (m_currentTextLength > 0) {
+        KDSize sizePreviousText = KDText::stringSize(m_textBuffer);
+        m_currentTextLength--;
+        m_textBuffer[m_currentTextLength] = 0;
+        KDSize sizeText = KDText::stringSize(m_textBuffer);
+        KDRect dirtyZone(sizeText.width(), 0, sizePreviousText.width()-sizeText.width(), sizeText.height());
+        markRectAsDirty(dirtyZone);
+      }
+      return true;
+    default:
+      if ((int)event >= 0x100) {
+        return false;
+      }
+      if (m_currentTextLength == 0 || m_currentTextLength-1 < m_textBufferSize) {
+        KDSize sizePreviousText = KDText::stringSize(m_textBuffer);
+        m_textBuffer[m_currentTextLength++] = (int)event;
+        m_textBuffer[m_currentTextLength] = 0;
+        KDSize sizeText = KDText::stringSize(m_textBuffer);
+        KDRect dirtyZone(sizePreviousText.width(), 0, sizeText.width()-sizePreviousText.width(), sizeText.height());
+        markRectAsDirty(dirtyZone);
+      }
+      return true;
   }
-  if (m_currentTextLength == 0 || m_currentTextLength-1 < m_textBufferSize) {
-    KDSize sizePreviousText = KDText::stringSize(m_textBuffer);
-    m_textBuffer[m_currentTextLength++] = (int)event;
-    m_textBuffer[m_currentTextLength] = 0;
-    KDSize sizeText = KDText::stringSize(m_textBuffer);
-    KDRect dirtyZone(sizePreviousText.width(), 0, sizeText.width()-sizePreviousText.width(), sizeText.height());
-    markRectAsDirty(dirtyZone);
-  }
-  return true;
 }
 
 const char * TextField::textBuffer () const {
@@ -53,6 +63,10 @@ const char * TextField::textBuffer () const {
   return textBuffer;
 }
 
+int TextField::bufferLength () const {
+  return m_currentTextLength;
+}
+
 void TextField::setTextBuffer(const char * text) {
   strlcpy(m_textBuffer, text, m_textBufferSize);
   m_currentTextLength = strlen(text);