Index: uspace/lib/c/generic/ddi.c
===================================================================
--- uspace/lib/c/generic/ddi.c	(revision 9f4067b6fe005421ad7a874724f2a19810a60e68)
+++ uspace/lib/c/generic/ddi.c	(revision 665903719ace3b07b3fc2f8d58eb880c7ce27b8d)
@@ -136,5 +136,5 @@
  * @param size     Size of the I/O region.
  * @param virt     Virtual address for application's
- *                 PIO operations.
+ *                 PIO operations. Can be NULL for PMIO.
  *
  * @return EOK on success.
@@ -146,9 +146,12 @@
 #ifdef IO_SPACE_BOUNDARY
 	if (pio_addr < IO_SPACE_BOUNDARY) {
-		*virt = pio_addr;
+		if (virt)
+			*virt = pio_addr;
 		return iospace_enable(task_get_id(), pio_addr, size);
 	}
 #endif
-	
+	if (!virt)
+		return EINVAL;
+
 	void *phys_frame =
 	    (void *) ALIGN_DOWN((uintptr_t) pio_addr, PAGE_SIZE);