diff --git a/src/she/event.h b/src/she/event.h
index 105e15ebf1..3131c64939 100644
--- a/src/she/event.h
+++ b/src/she/event.h
@@ -46,7 +46,9 @@ namespace she {
       NoneButton,
       LeftButton,
       RightButton,
-      MiddleButton
+      MiddleButton,
+      X1Button,
+      X2Button,
     };
 
     typedef std::vector<std::string> Files;
diff --git a/src/she/win/window.h b/src/she/win/window.h
index 925fe54277..59ce7a8ed3 100644
--- a/src/she/win/window.h
+++ b/src/she/win/window.h
@@ -1,5 +1,5 @@
 // SHE library
-// Copyright (C) 2012-2016  David Capello
+// Copyright (C) 2012-2017  David Capello
 //
 // This file is released under the terms of the MIT license.
 // Read LICENSE.txt for more information.
@@ -458,7 +458,8 @@ namespace she {
 
         case WM_LBUTTONDOWN:
         case WM_RBUTTONDOWN:
-        case WM_MBUTTONDOWN: {
+        case WM_MBUTTONDOWN:
+        case WM_XBUTTONDOWN: {
           Event ev;
           ev.setType(Event::MouseDown);
           ev.setModifiers(get_modifiers_from_last_win32_message());
@@ -468,7 +469,10 @@ namespace she {
           ev.setButton(
             msg == WM_LBUTTONDOWN ? Event::LeftButton:
             msg == WM_RBUTTONDOWN ? Event::RightButton:
-            msg == WM_MBUTTONDOWN ? Event::MiddleButton: Event::NoneButton);
+            msg == WM_MBUTTONDOWN ? Event::MiddleButton:
+            msg == WM_XBUTTONDOWN && GET_XBUTTON_WPARAM(wparam) == 1 ? Event::X1Button:
+            msg == WM_XBUTTONDOWN && GET_XBUTTON_WPARAM(wparam) == 2 ? Event::X2Button:
+            Event::NoneButton);
 
           if (m_pointerType != PointerType::Unknown) {
             ev.setPointerType(m_pointerType);
@@ -481,7 +485,8 @@ namespace she {
 
         case WM_LBUTTONUP:
         case WM_RBUTTONUP:
-        case WM_MBUTTONUP: {
+        case WM_MBUTTONUP:
+        case WM_XBUTTONUP: {
           Event ev;
           ev.setType(Event::MouseUp);
           ev.setModifiers(get_modifiers_from_last_win32_message());
@@ -491,7 +496,10 @@ namespace she {
           ev.setButton(
             msg == WM_LBUTTONUP ? Event::LeftButton:
             msg == WM_RBUTTONUP ? Event::RightButton:
-            msg == WM_MBUTTONUP ? Event::MiddleButton: Event::NoneButton);
+            msg == WM_MBUTTONUP ? Event::MiddleButton:
+            msg == WM_XBUTTONUP && GET_XBUTTON_WPARAM(wparam) == 1 ? Event::X1Button:
+            msg == WM_XBUTTONUP && GET_XBUTTON_WPARAM(wparam) == 2 ? Event::X2Button:
+            Event::NoneButton);
 
           if (m_pointerType != PointerType::Unknown) {
             ev.setPointerType(m_pointerType);
@@ -509,7 +517,8 @@ namespace she {
 
         case WM_LBUTTONDBLCLK:
         case WM_MBUTTONDBLCLK:
-        case WM_RBUTTONDBLCLK: {
+        case WM_RBUTTONDBLCLK:
+        case WM_XBUTTONDBLCLK: {
           Event ev;
           ev.setType(Event::MouseDoubleClick);
           ev.setModifiers(get_modifiers_from_last_win32_message());
@@ -519,7 +528,10 @@ namespace she {
           ev.setButton(
             msg == WM_LBUTTONDBLCLK ? Event::LeftButton:
             msg == WM_RBUTTONDBLCLK ? Event::RightButton:
-            msg == WM_MBUTTONDBLCLK ? Event::MiddleButton: Event::NoneButton);
+            msg == WM_MBUTTONDBLCLK ? Event::MiddleButton:
+            msg == WM_XBUTTONDBLCLK && GET_XBUTTON_WPARAM(wparam) == 1 ? Event::X1Button:
+            msg == WM_XBUTTONDBLCLK && GET_XBUTTON_WPARAM(wparam) == 2 ? Event::X2Button:
+            Event::NoneButton);
 
           if (m_pointerType != PointerType::Unknown) {
             ev.setPointerType(m_pointerType);
diff --git a/src/ui/manager.cpp b/src/ui/manager.cpp
index 6bad21f785..d637e75c74 100644
--- a/src/ui/manager.cpp
+++ b/src/ui/manager.cpp
@@ -264,6 +264,8 @@ static MouseButtons mouse_buttons_from_she_to_ui(const she::Event& sheEvent)
     case she::Event::LeftButton:   return kButtonLeft; break;
     case she::Event::RightButton:  return kButtonRight; break;
     case she::Event::MiddleButton: return kButtonMiddle; break;
+    case she::Event::X1Button:     return kButtonX1; break;
+    case she::Event::X2Button:     return kButtonX2; break;
     default: return kButtonNone;
   }
 }
diff --git a/src/ui/mouse_buttons.h b/src/ui/mouse_buttons.h
index 86a3c00490..6509e421b8 100644
--- a/src/ui/mouse_buttons.h
+++ b/src/ui/mouse_buttons.h
@@ -1,5 +1,5 @@
 // Aseprite UI Library
-// Copyright (C) 2001-2013  David Capello
+// Copyright (C) 2001-2017  David Capello
 //
 // This file is released under the terms of the MIT license.
 // Read LICENSE.txt for more information.
@@ -14,7 +14,9 @@ namespace ui {
     kButtonNone = 0,
     kButtonLeft = 1,
     kButtonRight = 2,
-    kButtonMiddle = 4
+    kButtonMiddle = 4,
+    kButtonX1 = 8,
+    kButtonX2 = 16,
   };
 
 } // namespace ui