diff --git a/binding-mri/input-binding.cpp b/binding-mri/input-binding.cpp
index 41f3ce1..18e161a 100644
--- a/binding-mri/input-binding.cpp
+++ b/binding-mri/input-binding.cpp
@@ -156,7 +156,9 @@ static buttonCodes[] =
 
 	{ "MOUSELEFT",   Input::MouseLeft   },
 	{ "MOUSEMIDDLE", Input::MouseMiddle },
-	{ "MOUSERIGHT",  Input::MouseRight  }
+	{ "MOUSERIGHT",  Input::MouseRight  },
+	{ "MOUSEX1",     Input::MouseX1     },
+	{ "MOUSEX2",     Input::MouseX2     }
 };
 
 static elementsN(buttonCodes);
diff --git a/doc/extension_doc.md b/doc/extension_doc.md
index 1e14f44..98085a8 100644
--- a/doc/extension_doc.md
+++ b/doc/extension_doc.md
@@ -19,6 +19,10 @@ returns: Integer
 
 Returns the cumulative amount of scroll events (negative if down, positive if up) inbetween the current and last `Input.update` call.
 
+## Input::MOUSEX1 / ::MOUSEX2
+
+These two constants representing two extra mouse buttons can be passed to the familiar #press?/#trigger?/#repeat? functions.
+
 ## MKXP.data_directory()
 returns: String  
 
diff --git a/src/input.cpp b/src/input.cpp
index f025b5c..1dcbe55 100644
--- a/src/input.cpp
+++ b/src/input.cpp
@@ -34,7 +34,7 @@
 #include <string.h>
 #include <assert.h>
 
-#define BUTTON_CODE_COUNT 24
+#define BUTTON_CODE_COUNT 26
 
 struct ButtonState
 {
@@ -237,7 +237,7 @@ static const int mapToIndex[] =
 	0,
 	16, 17, 18, 19, 20,
 	0, 0, 0, 0, 0, 0, 0, 0,
-	21, 22, 23
+	21, 22, 23, 24, 25
 };
 
 static elementsN(mapToIndex);
@@ -465,12 +465,14 @@ struct InputPrivate
 
 	void initMsBindings()
 	{
-		msBindings.resize(3);
+		msBindings.resize(5);
 
 		size_t i = 0;
 		msBindings[i++] = MsBinding(SDL_BUTTON_LEFT,   Input::MouseLeft);
 		msBindings[i++] = MsBinding(SDL_BUTTON_MIDDLE, Input::MouseMiddle);
 		msBindings[i++] = MsBinding(SDL_BUTTON_RIGHT,  Input::MouseRight);
+		msBindings[i++] = MsBinding(SDL_BUTTON_X1,     Input::MouseX1);
+		msBindings[i++] = MsBinding(SDL_BUTTON_X2,     Input::MouseX2);
 	}
 
 	void pollBindings(Input::ButtonCode &repeatCand)
diff --git a/src/input.h b/src/input.h
index 1433855..a181919 100644
--- a/src/input.h
+++ b/src/input.h
@@ -43,7 +43,8 @@ public:
 		F5 = 25, F6 = 26, F7 = 27, F8 = 28, F9 = 29,
 
 		/* Non-standard extensions */
-		MouseLeft = 38, MouseMiddle = 39, MouseRight = 40
+		MouseLeft = 38, MouseMiddle = 39, MouseRight = 40,
+		MouseX1 = 41, MouseX2 = 42
 	};
 
 	void update();