diff --git a/src/fmessagebox.cpp b/src/fmessagebox.cpp
index 4d0396be..a91c13da 100644
--- a/src/fmessagebox.cpp
+++ b/src/fmessagebox.cpp
@@ -108,7 +108,7 @@ FMessageBox& FMessageBox::operator = (const FMessageBox& mbox)
   }
   else
   {
-    for (uInt n{0}; n < num_buttons && button[n]; n++)
+    for (std::size_t n{0}; n < num_buttons && n < MAX_BUTTONS; n++)
       delete button[n];
 
     if ( mbox.getParentWidget() )
@@ -138,7 +138,7 @@ void FMessageBox::setHeadline (const FString& headline)
   headline_text.setString(headline);
   setHeight(getHeight() + 2, true);
 
-  for (uInt n{0}; n < num_buttons && button[n]; n++)
+  for (std::size_t n{0}; n < num_buttons && n < MAX_BUTTONS; n++)
     button[n]->setY (int(getHeight()) - 4, false);
 
   const std::size_t column_width = getColumnWidth(headline_text);
@@ -268,7 +268,7 @@ inline void FMessageBox::allocation()
 //----------------------------------------------------------------------
 inline void FMessageBox::deallocation()
 {
-  for (uInt n{0}; n < num_buttons && button[n]; n++)
+  for (std::size_t n{0}; n < num_buttons && n < MAX_BUTTONS; n++)
     delete button[n];
 }
 
@@ -388,7 +388,7 @@ void FMessageBox::resizeButtons() const
   std::size_t len[3]{};
   std::size_t max_size{};
 
-  for (std::size_t n{0}; n < num_buttons && button[n]; n++)
+  for (std::size_t n{0}; n < num_buttons && n < MAX_BUTTONS; n++)
   {
     len[n] = button[n]->getText().getLength();
 
@@ -410,7 +410,7 @@ void FMessageBox::resizeButtons() const
   if ( max_size < 7 )
     max_size = 7;
 
-  for (std::size_t n{0}; n < num_buttons && button[n]; n++)
+  for (std::size_t n{0}; n < num_buttons && n < MAX_BUTTONS; n++)
     button[n]->setWidth(max_size + 3, false);
 }
 
@@ -420,7 +420,7 @@ void FMessageBox::adjustButtons()
   static constexpr std::size_t gap = 4;
   std::size_t btn_width{0};
 
-  for (std::size_t n{0}; n < num_buttons && button[n]; n++)
+  for (std::size_t n{0}; n < num_buttons && n < MAX_BUTTONS; n++)
   {
     if ( n == num_buttons - 1 )
       btn_width += button[n]->getWidth();
@@ -439,7 +439,7 @@ void FMessageBox::adjustButtons()
 
   const int btn_x = int((getWidth() - btn_width) / 2);
 
-  for (std::size_t n{0}; n < num_buttons && button[n]; n++)
+  for (std::size_t n{0}; n < num_buttons && n < MAX_BUTTONS; n++)
   {
     if ( n == 0 )
       button[n]->setX(btn_x);
diff --git a/src/include/final/fmessagebox.h b/src/include/final/fmessagebox.h
index dfdfebf6..22a63bfa 100644
--- a/src/include/final/fmessagebox.h
+++ b/src/include/final/fmessagebox.h
@@ -137,6 +137,9 @@ class FMessageBox : public FDialog
     void                cb_processClick (int);
 
   private:
+    // Constants
+    static constexpr std::size_t MAX_BUTTONS = 3;
+
     // Methods
     void                init();
     void                allocation();
@@ -151,11 +154,11 @@ class FMessageBox : public FDialog
     FString       headline_text{};
     FString       text{};
     FStringList   text_components{};
-    FButton*      button[3]{nullptr};
+    FButton*      button[MAX_BUTTONS]{nullptr};
     std::size_t   max_line_width{0};
     FColor        emphasis_color{getColorTheme()->dialog_emphasis_fg};
-    int           button_digit[3]{0};
-    uInt          num_buttons{0};
+    int           button_digit[MAX_BUTTONS]{0};
+    std::size_t   num_buttons{0};
     std::size_t   text_num_lines{0};
     bool          center_text{false};
 };
diff --git a/src/include/final/fwidget.h b/src/include/final/fwidget.h
index b16a488a..13e76fc2 100644
--- a/src/include/final/fwidget.h
+++ b/src/include/final/fwidget.h
@@ -320,7 +320,7 @@ class FWidget : public FVTerm, public FObject
     void                     addCallback (const FString&, Args&&...);
     template<typename... Args>
     void                     delCallback (Args&&...);
-    void                     emitCallback (const FString&);
+    void                     emitCallback (const FString&) const;
     void                     addAccelerator (FKey);
     virtual void             addAccelerator (FKey, FWidget*);
     void                     delAccelerator ();
@@ -997,7 +997,7 @@ inline void FWidget::delCallback (Args&&... args)
 }
 
 //----------------------------------------------------------------------
-inline void FWidget::emitCallback (const FString& emit_signal)
+inline void FWidget::emitCallback (const FString& emit_signal) const
 {
   callback_impl.emitCallback(emit_signal);
 }