diff --git a/sp/src/public/vgui/MouseCode.h b/sp/src/public/vgui/MouseCode.h
index 7ba16214..9b13fc81 100644
--- a/sp/src/public/vgui/MouseCode.h
+++ b/sp/src/public/vgui/MouseCode.h
@@ -18,6 +18,15 @@
 namespace vgui
 {
 typedef ButtonCode_t MouseCode;
+
+static inline int MouseButtonBit(MouseCode code)
+{
+	if (code < MOUSE_FIRST || code > MOUSE_LAST) {
+		Assert(false);
+		return 0;
+	}
+	return 1 << (code - MOUSE_FIRST);
+}
 }
 
 #endif // MOUSECODE_H
diff --git a/sp/src/vgui2/vgui_controls/Button.cpp b/sp/src/vgui2/vgui_controls/Button.cpp
index cceb8043..406c3e13 100644
--- a/sp/src/vgui2/vgui_controls/Button.cpp
+++ b/sp/src/vgui2/vgui_controls/Button.cpp
@@ -695,12 +695,12 @@ void Button::SetMouseClickEnabled(MouseCode code,bool state)
 	if(state)
 	{
 		//set bit to 1
-		_mouseClickMask|=1<<((int)(code+1));
+		_mouseClickMask|=MouseButtonBit(code);
 	}
 	else
 	{
 		//set bit to 0
-		_mouseClickMask&=~(1<<((int)(code+1)));
+		_mouseClickMask&=~MouseButtonBit(code);
 	}	
 }
 
@@ -709,7 +709,7 @@ void Button::SetMouseClickEnabled(MouseCode code,bool state)
 //-----------------------------------------------------------------------------
 bool Button::IsMouseClickEnabled(MouseCode code)
 {
-	if(_mouseClickMask&(1<<((int)(code+1))))
+	if(_mouseClickMask&MouseButtonBit(code))
 	{
 		return true;
 	}