Index: sys/dev/aacraid/aacraid.c
===================================================================
--- sys/dev/aacraid/aacraid.c
+++ sys/dev/aacraid/aacraid.c
@@ -579,7 +579,7 @@
 			       BUS_SPACE_MAXADDR_32BIT,	/* lowaddr */
 			       BUS_SPACE_MAXADDR, 	/* highaddr */
 			       NULL, NULL, 		/* filter, filterarg */
-			       sc->aac_max_sectors << 9, /* maxsize */
+			       AAC_MAXIO_SIZE(sc),	/* maxsize */
 			       sc->aac_sg_tablesize,	/* nsegments */
 			       BUS_SPACE_MAXSIZE_32BIT,	/* maxsegsize */
 			       BUS_DMA_ALLOCNOW,	/* flags */
@@ -1807,7 +1807,7 @@
 	}
 
 	ip->MaxIoCommands = sc->aac_max_fibs;
-	ip->MaxIoSize = sc->aac_max_sectors << 9;
+	ip->MaxIoSize = AAC_MAXIO_SIZE(sc);
 	ip->MaxFibSize = sc->aac_max_fib_size;
 
 	aac_adapter_init_tole(ip);
Index: sys/dev/aacraid/aacraid_cam.c
===================================================================
--- sys/dev/aacraid/aacraid_cam.c
+++ sys/dev/aacraid/aacraid_cam.c
@@ -1011,7 +1011,7 @@
 		cpi->max_lun = 7;	/* Per the controller spec */
 		cpi->initiator_id = camsc->inf->InitiatorBusId;
 		cpi->bus_id = camsc->inf->BusNumber;
-		cpi->maxio = sc->aac_max_sectors << 9;
+		cpi->maxio = AAC_MAXIO_SIZE(sc);
 
 		/*
 		 * Resetting via the passthrough or parallel bus scan
Index: sys/dev/aacraid/aacraid_var.h
===================================================================
--- sys/dev/aacraid/aacraid_var.h
+++ sys/dev/aacraid/aacraid_var.h
@@ -470,6 +470,14 @@
 	u_int32_t	FwDebugBufferSize;	/* FW Debug Buffer size */	
 };
 
+/*
+ * Max. I/O size in bytes.
+ * Reserve one page for the DMA subsystem, that may need it when the
+ * I/O buffer is not page aligned.
+ */
+#define AAC_MAXIO_SIZE(sc)	MIN(((sc)->aac_max_sectors << 9) - PAGE_SIZE, \
+					maxphys)
+
 /*
  * Event callback mechanism for the driver
  */