diff --git a/src/add-ons/accelerants/matrox/GetModeInfo.c b/src/add-ons/accelerants/matrox/GetModeInfo.c
index 22a18323c6..3cf3eda63d 100644
--- a/src/add-ons/accelerants/matrox/GetModeInfo.c
+++ b/src/add-ons/accelerants/matrox/GetModeInfo.c
@@ -4,7 +4,7 @@
 
 	Other authors:
 	Mark Watson
-	Rudolf Cornelissen 9-11/2002
+	Rudolf Cornelissen 9-11/2005
 */
 
 #define MODULE_BIT 0x02000000
@@ -140,5 +140,8 @@ status_t GET_PIXEL_CLOCK_LIMITS(display_mode *dm, uint32 *low, uint32 *high)
 /* Return the semaphore id that will be used to signal a vertical sync occured.  */
 sem_id ACCELERANT_RETRACE_SEMAPHORE(void)
 {
-	return si->vblank;
+	if (si->ps.int_assigned)
+		return si->vblank;
+	else
+		return B_ERROR;
 }
diff --git a/src/add-ons/accelerants/matrox/ProposeDisplayMode.c b/src/add-ons/accelerants/matrox/ProposeDisplayMode.c
index 9d0baaee1e..c5c6b3949b 100644
--- a/src/add-ons/accelerants/matrox/ProposeDisplayMode.c
+++ b/src/add-ons/accelerants/matrox/ProposeDisplayMode.c
@@ -378,6 +378,12 @@ status_t PROPOSE_DISPLAY_MODE(display_mode *target, const display_mode *low, con
 		}
 	}
 
+	/* if not dualhead capable card clear dualhead flags */
+	if (!(target->flags & DUALHEAD_CAPABLE))
+	{
+		target->flags &= ~DUALHEAD_BITS;
+	}
+
 	/* set TV_CAPABLE if suitable: pixelclock is not important (defined by TVstandard) */
 	switch (si->ps.card_type)
 	{
@@ -412,6 +418,12 @@ status_t PROPOSE_DISPLAY_MODE(display_mode *target, const display_mode *low, con
 		break;
 	}
 
+	/* if not TVout capable card clear TVout flags */
+	if (!(target->flags & TV_CAPABLE))
+	{
+		target->flags &= ~TV_BITS;
+	}
+
 	/* fixme: currently the matrox driver can only do secondary TVout */
 	target->flags &= ~TV_PRIMARY;
 
@@ -423,7 +435,7 @@ status_t PROPOSE_DISPLAY_MODE(display_mode *target, const display_mode *low, con
 	if (si->ps.card_type >= G200)
 		target->flags |= B_SUPPORTS_OVERLAYS;
 
-	LOG(1, ("PROPOSEMODE: validated status modeflags: $%08x\n", target->flags));
+	LOG(1, ("PROPOSEMODE: validated modeflags: $%08x\n", target->flags));
 
 	/* overrule timing command flags to be (fixed) blank_pedestal = 0.0IRE,
 	 * progressive scan (fixed), and setup sync_on_green flag according to
diff --git a/src/add-ons/accelerants/matrox/SetDisplayMode.c b/src/add-ons/accelerants/matrox/SetDisplayMode.c
index 3e13bdb466..923d1736be 100644
--- a/src/add-ons/accelerants/matrox/SetDisplayMode.c
+++ b/src/add-ons/accelerants/matrox/SetDisplayMode.c
@@ -5,7 +5,7 @@
 	Other authors:
 	Mark Watson,
 	Apsed,
-	Rudolf Cornelissen 11/2002-2/2004
+	Rudolf Cornelissen 11/2002-11/2005
 */
 
 #define MODULE_BIT 0x00200000
@@ -20,11 +20,14 @@ static void interrupt_enable(bool flag) {
 	status_t result;
 	gx00_set_bool_state sbs;
 
-	/* set the magic number so the driver knows we're for real */
-	sbs.magic = GX00_PRIVATE_DATA_MAGIC;
-	sbs.do_it = flag;
-	/* contact driver and get a pointer to the registers and shared data */
-	result = ioctl(fd, GX00_RUN_INTERRUPTS, &sbs, sizeof(sbs));
+	if (si->ps.int_assigned)
+	{
+		/* set the magic number so the driver knows we're for real */
+		sbs.magic = GX00_PRIVATE_DATA_MAGIC;
+		sbs.do_it = flag;
+		/* contact driver and get a pointer to the registers and shared data */
+		result = ioctl(fd, GX00_RUN_INTERRUPTS, &sbs, sizeof(sbs));
+	}
 }
 
 /* First validate the mode, then call lots of bit banging stuff to set the mode(s)! */
@@ -63,18 +66,6 @@ status_t SET_DISPLAY_MODE(display_mode *mode_to_set)
 	/* See BOUNDS WARNING above... */
 	if (PROPOSE_DISPLAY_MODE(&target, &target, &target) == B_ERROR)	return B_ERROR;
 
-	/* if not dualhead capable card clear dualhead flags */
-	if (!(target.flags & DUALHEAD_CAPABLE))
-	{
-		target.flags &= ~DUALHEAD_BITS;
-	}
-	/* if not TVout capable card clear TVout flags */
-	if (!(target.flags & TV_CAPABLE))
-	{
-		target.flags &= ~TV_BITS;
-	}
-	LOG(1, ("SETMODE: (CONT.) validated command modeflags: $%08x\n", target.flags));
-
 	/* overlay engine, cursor and MOVE_DISPLAY need to know the status even when
 	 * in singlehead mode */
 	si->switched_crtcs = false;
diff --git a/src/add-ons/accelerants/matrox/engine/mga_general.c b/src/add-ons/accelerants/matrox/engine/mga_general.c
index 2f12477fcb..a11bdfdd75 100644
--- a/src/add-ons/accelerants/matrox/engine/mga_general.c
+++ b/src/add-ons/accelerants/matrox/engine/mga_general.c
@@ -1,7 +1,7 @@
 /* Authors:
    Mark Watson 12/1999,
    Apsed,
-   Rudolf Cornelissen 10/2002-3/2004
+   Rudolf Cornelissen 10/2002-11/2005
 */
 
 #define MODULE_BIT 0x00008000
@@ -54,7 +54,13 @@ status_t gx00_general_powerup()
 	status_t status;
 	uint32 card_class;
 
-	LOG(1,("POWERUP: Haiku Matrox Accelerant 0.23 running.\n"));
+	LOG(1,("POWERUP: Haiku Matrox Accelerant 0.24 running.\n"));
+
+	/* log VBLANK INT usability status */
+	if (si->ps.int_assigned)
+		LOG(4,("POWERUP: Usable INT assigned to HW; Vblank semaphore enabled\n"));
+	else
+		LOG(4,("POWERUP: No (usable) INT assigned to HW; Vblank semaphore disabled\n"));
 
 	/* detect card type and power it up */
 	switch(CFGR(DEVID))