diff -Naur xf86-input-mouse-1.2.3-orig/src/mouse.c xf86-input-mouse-1.2.3/src/mouse.c
--- xf86-input-mouse-1.2.3-orig/src/mouse.c	2007-09-19 23:17:25.000000000 +0200
+++ xf86-input-mouse-1.2.3/src/mouse.c	2008-10-07 15:31:02.000000000 +0200
@@ -1623,6 +1623,13 @@
 		 */
 		dz = ((signed char)(pBuf[5] << 1) +
 		      (signed char)(pBuf[6] << 1)) >> 1;
+		if (dz == 2) {
+		    dw = 1;
+		    dz = 0;
+		} else if (dz == -2) {
+		    dw = -1;
+		    dz = 0;
+		}
 		buttons |= (int)(~pBuf[7] & 0x7f) << 3;
 	    }
 	    break;