diff --git a/docs/changes.txt b/docs/changes.txt
index 423d79f114..d2b8473fc8 100644
--- a/docs/changes.txt
+++ b/docs/changes.txt
@@ -78,6 +78,7 @@ wxGTK:
 wxMSW:
 
 - Fix hang after clearing wxTAB_TRAVERSAL style on a window with children.
+- Fix handling of AUX2 mouse button events (Trylz).
 
 
 3.1.1: (released 2018-02-19)
diff --git a/src/msw/window.cpp b/src/msw/window.cpp
index ca8fccb9da..113b3b715d 100644
--- a/src/msw/window.cpp
+++ b/src/msw/window.cpp
@@ -5547,7 +5547,7 @@ bool wxWindowMSW::HandleMouseEvent(WXUINT msg, int x, int y, WXUINT flags)
         case WM_XBUTTONDOWN:
         case WM_XBUTTONUP:
         case WM_XBUTTONDBLCLK:
-            if ( flags & MK_XBUTTON2 )
+            if (HIWORD(flags) == XBUTTON2)
                 msg += wxEVT_AUX2_DOWN - wxEVT_AUX1_DOWN;
     }