diff --git a/shared-core/nouveau_fifo.c b/shared-core/nouveau_fifo.c
index c662165b..b6fc613c 100644
--- a/shared-core/nouveau_fifo.c
+++ b/shared-core/nouveau_fifo.c
@@ -403,6 +403,10 @@ static int nouveau_fifo_alloc(drm_device_t* dev,drm_nouveau_fifo_alloc_t* init,
 				NV_DMA_ACCESS_RO,
 				NV_DMA_TARGET_VIDMEM);
 	}
+	if (!cb_obj) {
+		DRM_ERROR("unable to alloc object for command buffer\n");
+		return DRM_ERR(EINVAL);
+	}
 	dev_priv->fifos[i].cmdbuf_obj = cb_obj;
 
 	/* that fifo is used */
@@ -536,7 +540,7 @@ void nouveau_fifo_cleanup(drm_device_t* dev, DRMFILE filp)
 
 	DRM_DEBUG("clearing FIFO enables from filp\n");
 	for(i=0;i<nouveau_fifo_number(dev);i++)
-		if (dev_priv->fifos[i].filp==filp)
+		if (dev_priv->fifos[i].used && dev_priv->fifos[i].filp==filp)
 			nouveau_fifo_free(dev,i);
 
 	/* check we still point at an active channel */
@@ -560,7 +564,7 @@ int nouveau_fifo_id_get(drm_device_t* dev, DRMFILE filp)
 	int i;
 
 	for(i=0;i<nouveau_fifo_number(dev);i++)
-		if (dev_priv->fifos[i].filp == filp)
+		if (dev_priv->fifos[i].used && dev_priv->fifos[i].filp == filp)
 			return i;
 	return -1;
 }
diff --git a/shared-core/nouveau_irq.c b/shared-core/nouveau_irq.c
index 6de4a5e4..160016ea 100644
--- a/shared-core/nouveau_irq.c
+++ b/shared-core/nouveau_irq.c
@@ -306,8 +306,33 @@ static void nouveau_pgraph_irq_handler(drm_device_t *dev)
 	}
 
 	if (status & NV_PGRAPH_INTR_ERROR) {
+		uint32_t nsource, nstatus, instance;
+		uint32_t address;
+		uint32_t channel;
+		uint32_t method, subc, data;
+
 		DRM_ERROR("NV: PGRAPH error interrupt\n");
 
+		nstatus = NV_READ(0x00400104);
+		nsource = NV_READ(0x00400108);
+		DRM_DEBUG("nsource:0x%08x\tnstatus:0x%08x\n", nsource, nstatus);
+
+		instance = NV_READ(0x00400158);
+		DRM_DEBUG("instance:0x%08x\n", instance);
+
+		address = NV_READ(0x400704);
+		data    = NV_READ(0x400708);
+		channel = (address >> 20) & 0x1F;
+		subc    = (address >> 16) & 0x7;
+		method  = address & 0x1FFC;
+		DRM_DEBUG("NV: 0x400704 = 0x%08x\n", address);
+		DRM_ERROR("NV: Channel %d/%d (class 0x%04x) -"
+			  "Method 0x%04x, Data 0x%08x\n",
+				channel, subc,
+				NV_READ(0x400160+subc*4) & 0xFFFF,
+				method, data
+			 );
+
 		status &= ~NV_PGRAPH_INTR_ERROR;
 		NV_WRITE(NV_PGRAPH_INTSTAT, NV_PGRAPH_INTR_ERROR);
 	}
@@ -360,6 +385,8 @@ irqreturn_t nouveau_irq_handler(DRM_IRQ_ARGS)
 	uint32_t status;
 
 	status = NV_READ(NV_PMC_INTSTAT);
+	if (!status)
+		return IRQ_NONE;
 
 	DRM_DEBUG("PMC INTSTAT: 0x%08x\n", status);
 
diff --git a/shared-core/nouveau_object.c b/shared-core/nouveau_object.c
index abd8bec5..0db92ec4 100644
--- a/shared-core/nouveau_object.c
+++ b/shared-core/nouveau_object.c
@@ -523,6 +523,8 @@ int nouveau_ioctl_object_init(DRM_IOCTL_ARGS)
 	int fifo;
 
 	fifo = nouveau_fifo_id_get(dev, filp);
+	if (fifo == -1)
+		return DRM_ERR(EINVAL);
 
 	DRM_COPY_FROM_USER_IOCTL(init, (drm_nouveau_object_init_t __user *)
 		data, sizeof(init));
@@ -577,6 +579,8 @@ int nouveau_ioctl_dma_object_init(DRM_IOCTL_ARGS)
 	int fifo;
 
 	fifo = nouveau_fifo_id_get(dev, filp);
+	if (fifo == -1)
+		return DRM_ERR(EINVAL);
 
 	DRM_COPY_FROM_USER_IOCTL(init, (drm_nouveau_dma_object_init_t __user *)
 		data, sizeof(init));