Index: win/tkWinPointer.c
==================================================================
--- win/tkWinPointer.c
+++ win/tkWinPointer.c
@@ -78,10 +78,16 @@
     if (GetKeyState(VK_MBUTTON) & 0x8000) {
 	state |= Button2Mask;
     }
     if (GetKeyState(VK_RBUTTON) & 0x8000) {
 	state |= Button3Mask;
+    }
+    if (GetKeyState(VK_XBUTTON1) & 0x8000) {
+	state |= Button4Mask;
+    }
+    if (GetKeyState(VK_XBUTTON2) & 0x8000) {
+	state |= Button5Mask;
     }
     return state;
 }
 
 /*

Index: win/tkWinX.c
==================================================================
--- win/tkWinX.c
+++ win/tkWinX.c
@@ -928,13 +928,16 @@
     case WM_LBUTTONDBLCLK:
     case WM_MBUTTONDOWN:
     case WM_MBUTTONDBLCLK:
     case WM_RBUTTONDOWN:
     case WM_RBUTTONDBLCLK:
+    case WM_XBUTTONDOWN:
+    case WM_XBUTTONDBLCLK:
     case WM_LBUTTONUP:
     case WM_MBUTTONUP:
     case WM_RBUTTONUP:
+    case WM_XBUTTONUP:
     case WM_MOUSEMOVE:
 	Tk_PointerEvent(hwnd, (short) LOWORD(lParam), (short) HIWORD(lParam));
 	return 1;
 
     case WM_SYSKEYDOWN:
@@ -1781,10 +1784,18 @@
 	break;
     case Button3:
 	msg = WM_RBUTTONDOWN;
 	wparam = MK_RBUTTON;
 	break;
+    case Button4:
+	msg = WM_XBUTTONDOWN;
+	wparam = MAKEWPARAM(MK_XBUTTON1, XBUTTON1);
+	break;
+    case Button5:
+	msg = WM_XBUTTONDOWN;
+	wparam = MAKEWPARAM(MK_XBUTTON2, XBUTTON2);
+	break;
     default:
 	return 0;
     }
 
     if (eventPtr->xbutton.state & Button1Mask) {
@@ -1793,10 +1804,16 @@
     if (eventPtr->xbutton.state & Button2Mask) {
 	wparam |= MK_MBUTTON;
     }
     if (eventPtr->xbutton.state & Button3Mask) {
 	wparam |= MK_RBUTTON;
+    }
+    if (eventPtr->xbutton.state & Button4Mask) {
+	wparam |= MK_XBUTTON1;
+    }
+    if (eventPtr->xbutton.state & Button5Mask) {
+	wparam |= MK_XBUTTON2;
     }
     if (eventPtr->xbutton.state & ShiftMask) {
 	wparam |= MK_SHIFT;
     }
     if (eventPtr->xbutton.state & ControlMask) {