Index: drivers/input/i8042prt/keyboard.c
===================================================================
--- drivers/input/i8042prt/keyboard.c	(revision 74227)
+++ drivers/input/i8042prt/keyboard.c	(working copy)
@@ -369,7 +369,7 @@
 		DeviceExtension->KeyboardBuffer + KeysInBufferCopy,
 		&KeysTransferred);
 
-	KeAcquireInterruptSpinLock(PortDeviceExtension->HighestDIRQLInterrupt);
+	Irql = KeAcquireInterruptSpinLock(PortDeviceExtension->HighestDIRQLInterrupt);
 	DeviceExtension->KeysInBuffer -= KeysTransferred;
 	KeReleaseInterruptSpinLock(PortDeviceExtension->HighestDIRQLInterrupt, Irql);
 }
Index: drivers/input/i8042prt/pnp.c
===================================================================
--- drivers/input/i8042prt/pnp.c	(revision 74227)
+++ drivers/input/i8042prt/pnp.c	(working copy)
@@ -303,8 +303,11 @@
         return Status;
     }
 
-    if (DirqlMax == PortDeviceExtension->KeyboardInterrupt.Dirql)
+    if (!PortDeviceExtension->HighestDIRQLInterrupt ||
+       (PortDeviceExtension->HighestDIRQLInterrupt && PortDeviceExtension->KeyboardInterrupt.Dirql > PortDeviceExtension->HighestDIRQLInterrupt->Irql))
+    {
         PortDeviceExtension->HighestDIRQLInterrupt = PortDeviceExtension->KeyboardInterrupt.Object;
+    }
     PortDeviceExtension->Flags |= KEYBOARD_INITIALIZED;
     return STATUS_SUCCESS;
 }
@@ -353,9 +356,11 @@
         goto cleanup;
     }
 
-    if (DirqlMax == PortDeviceExtension->MouseInterrupt.Dirql)
+    if (!PortDeviceExtension->HighestDIRQLInterrupt ||
+       (PortDeviceExtension->HighestDIRQLInterrupt && PortDeviceExtension->MouseInterrupt.Dirql > PortDeviceExtension->HighestDIRQLInterrupt->Irql))
+    {
         PortDeviceExtension->HighestDIRQLInterrupt = PortDeviceExtension->MouseInterrupt.Object;
-
+    }
     PortDeviceExtension->Flags |= MOUSE_INITIALIZED;
     Status = STATUS_SUCCESS;
 
@@ -477,16 +482,23 @@
             WARN_(I8042PRT, "i8042ConnectMouseInterrupt failed: %lx\n", Status);
         }
 
-        /* Start the mouse */
-        Irql = KeAcquireInterruptSpinLock(DeviceExtension->HighestDIRQLInterrupt);
-        /* HACK: the mouse has already been reset in i8042DetectMouse. This second
-           reset prevents some touchpads/mice from working (Dell D531, D600).
-           See CORE-6901 */
-        if (!(i8042HwFlags & FL_INITHACK))
+        if (DeviceExtension->HighestDIRQLInterrupt)
         {
-            i8042IsrWritePort(DeviceExtension, MOU_CMD_RESET, CTRL_WRITE_MOUSE);
+            /* Start the mouse */
+            Irql = KeAcquireInterruptSpinLock(DeviceExtension->HighestDIRQLInterrupt);
+            /* HACK: the mouse has already been reset in i8042DetectMouse. This second
+               reset prevents some touchpads/mice from working (Dell D531, D600).
+               See CORE-6901 */
+            if (!(i8042HwFlags & FL_INITHACK))
+            {
+                i8042IsrWritePort(DeviceExtension, MOU_CMD_RESET, CTRL_WRITE_MOUSE);
+            }
+            KeReleaseInterruptSpinLock(DeviceExtension->HighestDIRQLInterrupt, Irql);
         }
-        KeReleaseInterruptSpinLock(DeviceExtension->HighestDIRQLInterrupt, Irql);
+        else
+        {
+            WARN_(I8042PRT, "HighestDIRQLInterrupt is null\n");
+        }
     }
 
     return Status;