diff --git a/src/add-ons/accelerants/nvidia/GetModeInfo.c b/src/add-ons/accelerants/nvidia/GetModeInfo.c
index ea1dd2561a..5a454d0c05 100644
--- a/src/add-ons/accelerants/nvidia/GetModeInfo.c
+++ b/src/add-ons/accelerants/nvidia/GetModeInfo.c
@@ -4,7 +4,7 @@
 
 	Other authors:
 	Mark Watson
-	Rudolf Cornelissen 9/2002-5/2003
+	Rudolf Cornelissen 9/2002-10/2005
 */
 
 #define MODULE_BIT 0x02000000
@@ -156,5 +156,8 @@ 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/nvidia/SetDisplayMode.c b/src/add-ons/accelerants/nvidia/SetDisplayMode.c
index 50ba1b0984..0487fb640b 100644
--- a/src/add-ons/accelerants/nvidia/SetDisplayMode.c
+++ b/src/add-ons/accelerants/nvidia/SetDisplayMode.c
@@ -17,15 +17,19 @@
 	Enable/Disable interrupts.  Just a wrapper around the
 	ioctl() to the kernel driver.
 */
-static void interrupt_enable(bool flag) {
-	status_t result;
+static void interrupt_enable(bool flag)
+{
+	status_t result = B_OK;
 	nv_set_bool_state sbs;
 
-	/* set the magic number so the driver knows we're for real */
-	sbs.magic = NV_PRIVATE_DATA_MAGIC;
-	sbs.do_it = flag;
-	/* contact driver and get a pointer to the registers and shared data */
-	result = ioctl(fd, NV_RUN_INTERRUPTS, &sbs, sizeof(sbs));
+	if (si->ps.int_assigned)
+	{
+		/* set the magic number so the driver knows we're for real */
+		sbs.magic = NV_PRIVATE_DATA_MAGIC;
+		sbs.do_it = flag;
+		/* contact driver and get a pointer to the registers and shared data */
+		result = ioctl(fd, NV_RUN_INTERRUPTS, &sbs, sizeof(sbs));
+	}
 }
 
 /* First validate the mode, then call lots of bit banging stuff to set the mode(s)! */
diff --git a/src/add-ons/accelerants/nvidia/engine/nv_general.c b/src/add-ons/accelerants/nvidia/engine/nv_general.c
index c41cebd63d..5375d145cd 100644
--- a/src/add-ons/accelerants/nvidia/engine/nv_general.c
+++ b/src/add-ons/accelerants/nvidia/engine/nv_general.c
@@ -1,7 +1,7 @@
 /* Authors:
    Mark Watson 12/1999,
    Apsed,
-   Rudolf Cornelissen 10/2002-9/2005
+   Rudolf Cornelissen 10/2002-10/2005
 */
 
 #define MODULE_BIT 0x00008000
@@ -91,7 +91,13 @@ status_t nv_general_powerup()
 {
 	status_t status;
 
-	LOG(1,("POWERUP: Haiku nVidia Accelerant 0.55 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"));
+
+	LOG(1,("POWERUP: Haiku nVidia Accelerant 0.56 running.\n"));
 
 	/* preset no laptop */
 	si->ps.laptop = false;
diff --git a/src/add-ons/accelerants/nvidia/engine/nv_info.c b/src/add-ons/accelerants/nvidia/engine/nv_info.c
index 4202b117e6..6bbb7c4706 100644
--- a/src/add-ons/accelerants/nvidia/engine/nv_info.c
+++ b/src/add-ons/accelerants/nvidia/engine/nv_info.c
@@ -1,7 +1,7 @@
 /* Read initialisation information from card */
 /* some bits are hacks, where PINS is not known */
 /* Author:
-   Rudolf Cornelissen 7/2003-9/2005
+   Rudolf Cornelissen 7/2003-10/2005
 */
 
 #define MODULE_BIT 0x00002000