diff --git a/reactos/subsystems/ntvdm/callback.c b/reactos/subsystems/ntvdm/callback.c
index d1ecaf3f436..6c7e552935f 100644
--- a/reactos/subsystems/ntvdm/callback.c
+++ b/reactos/subsystems/ntvdm/callback.c
@@ -7,6 +7,14 @@
  *                  Hermes Belusca-Maito (hermes.belusca@sfr.fr)
  */
 
+/******************************************************************************\
+|   WARNING! WARNING! WARNING! WARNING! WARNING! WARNING! WARNING! WARNING!
+|
+|   Callbacks support supposes implicitely that the callbacks are used
+|   in the SAME thread as the CPU thread, otherwise messing in parallel
+|   with the CPU registers is 100% prone to bugs!!
+\******************************************************************************/
+
 /* INCLUDES *******************************************************************/
 
 #define NDEBUG
diff --git a/reactos/subsystems/ntvdm/hardware/mouse.c b/reactos/subsystems/ntvdm/hardware/mouse.c
index 63399d90cce..65727d1e3e7 100644
--- a/reactos/subsystems/ntvdm/hardware/mouse.c
+++ b/reactos/subsystems/ntvdm/hardware/mouse.c
@@ -121,7 +121,7 @@ static VOID MouseGetPacket(PMOUSE_PACKET Packet)
 VOID MouseUpdatePosition(PCOORD NewPosition)
 {
     /* Update the counters */
-    HorzCounter += ((NewPosition->X - Position.X) * WidthMm * Resolution) / WidthPixels;
+    HorzCounter += ((NewPosition->X - Position.X) * WidthMm  * Resolution) / WidthPixels;
     VertCounter += ((NewPosition->Y - Position.Y) * HeightMm * Resolution) / HeightPixels;
 
     /* Update the position */