diff --git a/apps/shared.de.i18n b/apps/shared.de.i18n
index c714d8a1b..ddacaf43f 100644
--- a/apps/shared.de.i18n
+++ b/apps/shared.de.i18n
@@ -52,6 +52,7 @@ StandardDeviation = "Standardabweichung"
 Step = "Schrittwert"
 StorageMemoryFull1 = "Der Speicher ist voll. Löschen Sie"
 StorageMemoryFull2 = "von Daten und versuchen Sie es erneut."
+StoreExpressionNotAcceptedAsFunction = "The function cannot be a Store"
 SyntaxError = "Syntaxfehler"
 ToZoom = "Zoom: "
 Trigonometric = "Trigonometrisch"
diff --git a/apps/shared.en.i18n b/apps/shared.en.i18n
index 09dc23ff8..e76f52206 100644
--- a/apps/shared.en.i18n
+++ b/apps/shared.en.i18n
@@ -48,6 +48,7 @@ RoundAbscissa = "Integer"
 Sci = "sci/"
 SquareSum = "Sum of squares"
 StandardDeviation = "Standard deviation"
+StoreExpressionNotAcceptedAsFunction = "The function cannot be a Store"
 StatTab = "Stats"
 Step = "Step"
 StorageMemoryFull1 = "The memory is full."
diff --git a/apps/shared.es.i18n b/apps/shared.es.i18n
index f67f7748f..b16c6dc81 100644
--- a/apps/shared.es.i18n
+++ b/apps/shared.es.i18n
@@ -52,6 +52,7 @@ StatTab = "Medidas"
 Step = "Incremento"
 StorageMemoryFull1 = "La memoria esta llena."
 StorageMemoryFull2 = "Borre datos e intente de nuevo."
+StoreExpressionNotAcceptedAsFunction = "The function cannot be a Store"
 SyntaxError = "Error sintactico"
 ToZoom = "Zoom : "
 Trigonometric = "Trigonometrico"
diff --git a/apps/shared.fr.i18n b/apps/shared.fr.i18n
index a529c590a..c3b50e37e 100644
--- a/apps/shared.fr.i18n
+++ b/apps/shared.fr.i18n
@@ -52,6 +52,7 @@ StatTab = "Stats"
 Step = "Pas"
 StorageMemoryFull1 = "La mémoire est pleine."
 StorageMemoryFull2 = "Effacez des données et réessayez."
+StoreExpressionNotAcceptedAsFunction = "The function cannot be a Store"
 SyntaxError = "Attention a la syntaxe"
 ToZoom = "Zoomer : "
 Trigonometric = "Trigonometrique"
diff --git a/apps/shared.pt.i18n b/apps/shared.pt.i18n
index f9268bb03..8b18b58ba 100644
--- a/apps/shared.pt.i18n
+++ b/apps/shared.pt.i18n
@@ -52,6 +52,7 @@ StatTab = "Estat"
 Step = "Passo"
 StorageMemoryFull1 = "A memoria esta chéia."
 StorageMemoryFull2 = "Apage dados e tente novamente."
+StoreExpressionNotAcceptedAsFunction = "The function cannot be a Store"
 SyntaxError = "Erro de sintaxe"
 ToZoom = "Zoom : "
 Trigonometric = "Trigonometrico"
diff --git a/apps/shared/expression_field_delegate_app.cpp b/apps/shared/expression_field_delegate_app.cpp
index 035f8e289..d9d952c2b 100644
--- a/apps/shared/expression_field_delegate_app.cpp
+++ b/apps/shared/expression_field_delegate_app.cpp
@@ -32,7 +32,7 @@ bool ExpressionFieldDelegateApp::layoutFieldDidReceiveEvent(LayoutField * layout
       displayWarning(I18n::Message::SyntaxError);
       return true;
     }
-    if (unparsableText(buffer, layoutField)) {
+    if (!isAcceptableText(buffer, layoutField)) {
       return true;
     }
   }
diff --git a/apps/shared/storage_function_app.cpp b/apps/shared/storage_function_app.cpp
index 6e5ec3590..1eb267edd 100644
--- a/apps/shared/storage_function_app.cpp
+++ b/apps/shared/storage_function_app.cpp
@@ -67,4 +67,18 @@ void StorageFunctionApp::willBecomeInactive() {
   ::App::willBecomeInactive();
 }
 
+
+bool StorageFunctionApp::isAcceptableExpression(const Expression exp, Responder * responder) {
+  if (TextFieldDelegateApp::isAcceptableExpression(exp, responder)) {
+    assert(!exp.isUninitialized());
+    if (exp.type() == ExpressionNode::Type::Store) {
+      // We do not want to allow a function to be "3->a" or "5->f(x)"
+      responder->app()->displayWarning(I18n::Message::StoreExpressionNotAcceptedAsFunction);
+      return false;
+    }
+    return true;
+  }
+  return false;
+}
+
 }
diff --git a/apps/shared/storage_function_app.h b/apps/shared/storage_function_app.h
index 3f46b81b1..7aa0b63d2 100644
--- a/apps/shared/storage_function_app.h
+++ b/apps/shared/storage_function_app.h
@@ -37,6 +37,7 @@ public:
   void willBecomeInactive() override;
 protected:
   StorageFunctionApp(Container * container, Snapshot * snapshot, ViewController * rootViewController);
+  bool isAcceptableExpression(const Poincare::Expression expression, Responder * responder) override;
 };
 
 }
diff --git a/apps/shared/text_field_delegate_app.cpp b/apps/shared/text_field_delegate_app.cpp
index fd52d0789..3272220e1 100644
--- a/apps/shared/text_field_delegate_app.cpp
+++ b/apps/shared/text_field_delegate_app.cpp
@@ -27,7 +27,7 @@ bool TextFieldDelegateApp::textFieldShouldFinishEditing(TextField * textField, I
 
 bool TextFieldDelegateApp::textFieldDidReceiveEvent(TextField * textField, Ion::Events::Event event) {
   if (textField->isEditing() && textField->shouldFinishEditing(event)) {
-    if (unparsableText(textField->text(), textField)) {
+    if (!isAcceptableText(textField->text(), textField)) {
       return true;
     }
   }
@@ -54,13 +54,17 @@ bool TextFieldDelegateApp::isFinishingEvent(Ion::Events::Event event) {
   return event == Ion::Events::OK || event == Ion::Events::EXE;
 }
 
-bool TextFieldDelegateApp::unparsableText(const char * text, Responder * responder) {
+bool TextFieldDelegateApp::isAcceptableText(const char * text, Responder * responder) {
   Expression exp = Expression::parse(text);
+  return isAcceptableExpression(exp, responder);
+}
+
+bool TextFieldDelegateApp::isAcceptableExpression(const Expression exp, Responder * responder) {
   if (exp.isUninitialized()) {
     responder->app()->displayWarning(I18n::Message::SyntaxError);
-    return true;
+    return false;
   }
-  return false;
+  return true;
 }
 
 }
diff --git a/apps/shared/text_field_delegate_app.h b/apps/shared/text_field_delegate_app.h
index 91e76a651..a25f48fec 100644
--- a/apps/shared/text_field_delegate_app.h
+++ b/apps/shared/text_field_delegate_app.h
@@ -19,10 +19,10 @@ public:
   virtual bool textFieldDidReceiveEvent(TextField * textField, Ion::Events::Event event) override;
 protected:
   TextFieldDelegateApp(Container * container, Snapshot * snapshot, ViewController * rootViewController);
-protected:
   bool fieldDidReceiveEvent(EditableField * field, Responder * responder, Ion::Events::Event event);
   bool isFinishingEvent(Ion::Events::Event event);
-  bool unparsableText(const char * text, Responder * responder);
+  bool isAcceptableText(const char * text, Responder * responder);
+  virtual bool isAcceptableExpression(const Poincare::Expression expression, Responder * responder);
 };
 
 }